Sitting on my dads lap at 18....eww. makes me uncomfortable to even think about. Going on a trip with a parent by itself is fine to me, but I get what you mean when there is the icky mini wife dynamic involved. 

Let me get this straight.....Your H booked an all inclusive trip to Cancun for his daughters graduation gift and he's joining her? Why are you not going? Furthermore why does he have to go?

I really do not see anything wrong with that as a gift to his DD.  My mom did the same with all of her grandkids when they graduated.  No biggie.

 Now…sitting on his lap is barf worthy.  Gag.    

I think it is interesting that you are not invited in some sense or involved it decision making.  Where I'm coming from is what is the real message here from the SD or even ovall all? Maybe it is more about the accomadations that are throwing up red flags for me.  I don't know but it just sounds creepy to me. When I was 18 I just wanted to be with my friends. NO parents!  MY SD who is 26, YES, I said 26, still sits on her daddeeesss lap like a 6 year old. Her maturity level is much less than a 26 year old..   It is disgusting.  I told my husband that if he thought that it was gross when Ivanka did that to Trump then how is that different?  He always makes a comment about how weird the Trump/Ivanka relationship is.  He was not happy about me saying that but honestly, what is the difference?  At least Ivanka was younger?!!!  

It is interesting that the issue between tmy 26 year old SD is also the lack of boundaries.  When she comes over to our house it is like a dog marking its territory.  She is in every room, cupboard, closet , our bedroom closet, my clothing drawers, my drawers in the bathroom etc.,  Again - it just doesn't feel appropriate.  Good for you for making other plans. I don't get this either.

Once he's funded college (for all of his kids), repaired the bathroom, and funded his retirement, I'd have no objection to him taking a trip with his daughter. But, if he hasn't set aside her college money and is going on the trip I'd be really upset.

A trip itself doesn't seem strange to me. I took my youngest son on a trip for spring break in his senior year. We shared a room. I knew it would be the last trip we ever took together so we went someplace he wanted to go. We went to a city to see the sights. We had a great time and both of us remember it fondly (at least he says he does). 

It was our last trip. During college he didn't do trips. He worked when school was not in session. And after graduation, and he was working, he went alone or with friends. 

But, our trip did not leave a spouse at home. First husband had died several years before. If he had been alive there is no way we would have gone without him.

How much vacation time does he have? Is there any left for you and his other children?

i would be booking an all day spa experience on day one of their trip.  An all day make over on day two.  An all day trip to the highest rated hair salon on day 3. An all day fashion make over at the top designer clothing place in  your city on day 4. I would rent a killer high end luxury vehicle for every day DH is on his weird Lollita romantic trip to the all inclusive couples resort with SD and ... I would have the little one in an lux day care every day while you are pampering yourself.

All on DH's credit card.  

Have fun!!!!

It's not the trip itself that gives pause. It's the fact that the daughter does not act in an age appropriate way and that dad does not enforce age appropriate boundaries.

...she sat on her father's lap last night and squeeled like a 5 year old because she's "so excited for this trip of a lifetime ... daddee" ...

If she is sitting on his lap poolside, it will garner side glances and raised eyebrows from the other guests.

I took care of my father after my mother died.  At 60 and 85 we shared a room several times.   Neither of us paraded around half dressed.   I took him to several reunions. 

But this was what I did for him in his last years  not what he did for me. 

I see more of a generational issue.  Used to be (decades ago) at age 18 you couldn’t wait to graduate and get out of the home.  Very few daughters at that time would have thought of going on a vacay with daddy; it would have been seen as a waste of time and money and, yes, seen as odd.  Vacations, back then, were either for the entire family or married couples.

Now there is the term adultolescent to describe those from age 18 to age 30 to indicate that they may be more adult or they may be more adolescent, who knows?  Now you have daddies giving butterfly kisses to their 18-year-olds and even 30-year-olds still living in the home, and everyone is supposed to be okay with that.

Not to me and not to many others outside of the Millennial generation.  I’d use the term gross too, and it has nothing to do with mistrust or sex (psychotherapists still to tend to think in those Freudian terms).  It has to do with at age 19 I moved out and lived in my own apt. and had a full-time job.  It’s as hard for me to imagine an 18 YO and pops going on a private vacay together as it is for me to imagine an older man pushing an 18 YO in a baby buggy.

That’s not to say that the way generations view childhood, or adolescents or adulthood can’t change.  It is just that don’t expect the latter generations to gulp down the Koolaid so fast.  Some of us can’t help it that at one time we took and society took great pride in expecting age 18 to truly be the age of adulthood—meaning providing for yourself and avoiding waste.  However, now it is supposed to be okay or even expected? for daddy to be handing out butterfly kisses, suckers, cars, vacays, and rocking precious daughter in his lap at age 18+.

If that’s the Koolaid we have to drink, some of us want to drink that bitter Koolaid as slowly as possible.

I've been to Cancun many times, stayed at lots of AIs (All Inclusives) and while some are family orientated, some are party party party.

One place we stayed was a party place, but smaller and it wasn't very full. There were two particular couples that we watched daily (we like to people watch) and had a few conversations with. One was an older man, around 50 and a younger lady, around 22, they were a couple. At first they were mistaken for father and daughter. They were not impressed and made a scene of PDI, french kissing, ass grabbing, him piggy backing her in the pool.

The other couple were the same age wise, except that they were father and daughter! The first few days, daughter would sit on daddees lap and they would play in the pool and laugh and giggle and actually made fun of a larger woman at the pool. It wasn't until they realized that everyone thought they were a couple, like the other May/December couple that the father got upset. He got drunk and made a bit of a scene about how disgusting it was that he couldn't go on a vacation with his daughter without people thinking he was a dirty old man. The large lady he'd made fun of looked at him and told him that he and his daughter behaved exactly the same as the other couple, without the french kissing and ass grabbing. Shut him up pretty quickly and for the rest of the week we never saw her sitting on his lap.

To check out a college. I am sitting in my hotel room. And he has his own room. 

The issue is not a daddy-daughter vacation or one of who's footing the bill.  If DH and SD had healthy adult boundaries, this would be acceptable - BUT they absolutely don't. I remember your post about "the gift" and that was an overt statement of emotional enmeshment/incest. Yup..the word incest gets attention, but call a spade a spade. Incest is not always about physical sexuality, but lap-sitting daddy at that age comes close enough to crossing that line. 

I had similar issues with SD24, and it took me a while to put my finger on the uneasiness I felt and to find the words/terminology to discuss it with DH.  When I finally expressed my observations and concerns about SD's very forward and intimately disposed behavior, it brought everything to the surface. DH stewed for a while - he knew it was the truth, but had difficulty even talking about it for months.  Lap-sitting, wanting to travel alone for weeks with DH (as opposed to girlfriends/peers/boyfriend), telling DH he could sleep in the bed with her, hanging up bras and panties over DH's robe and boxers, sending DH romantic texts during late hours of the evening and more were not normal. DH was very uncomfortable and embarassed by her behavior but did not know how to stop it. The more DH made clear boundaries, the more aggressive and angry SD became - like a scorned lover (remember Glenn Close in Fatal Attraction...seriously). He received a card shortly after SD moved out of state...."when YOU are ready to come and visit me, I will buy you a plane ticket.  You can stay in my apartment. WE will have an awesome time together."  She has a tiny studio apartment. DH's response was to text, "SM and I have not decided when WE are going to visit."  

The problem is more deeply rooted than a trip to Cancun.  Your DH allows this behavior and seems to enjoy the enmeshment.  The rapport between DH and SD is far from being a healthy father-daughter bond. You obviously intuit/know that.  This will continue to create derision and division in your marriage until DH creates healthy, respectful adult boundaries. Albeit, he may be one of those fathers who will never see the emotional damage that enmeshment does and continue to behave like an idiot with arrested development.

Refusing to go on the trip is understandable, especially when you were not included in the decision-making. DH and you should have discussed this with YOUR input and feelings considered. He's got his head up his ass. Playing and partying with SD seem to be more important than the sanctity of your marriage.  

Going to a spa on his ticket is nice, but it's even better when you're not doing it as a revenge tactic. That's game playing and it doesn't do a damn thing to move this issue towards resolution.  It's a bandaid on a wound that will continue to fester.  

When I was in late teens and early 20s, occassionally people used to mistake my mom and I as a couple. No sitting in laps or french kissing of course. We would occassionally hold hands, walk arm in arm, I would (and still) open doors for her, or I would put my arm around her shoulders and her arm was around my waist when we were walking.  We never went on vacation just the two of us but we did travel together occassionally without dad or my little brother.

She and I would frequently leave a week or two ahead of dad and my brother for the States while bro finished up school.  Often we would go to my GP's to work on some project that my grandfathers might need help on. In my mom's home town there were a number of laughable events where newer residents of town who did not know my mom pr her family would comment on the age difference between she and I as a couple and long time town residents would call them on it.  "Why, that is XYZLMNOP and her son.  Don't be rude!"  Or... some extremely funny comment that had us and everyone else in ear shot laughing.  Including the mistaken town neophites.

One time of significant note was when we had to cancel an Australia trip due to a Dx of a precancerous uteran condition for my mom.  Dad (and mom) wanted mom with the oncologists and surgeons ASAP and my brother was still a few weeks from finishing school.  I accompanied mom to get her going on tests, Doc consults, etc and dad and my brother joined us just before mom had surgery when school was out for my brother.  There were some notable moments during that period regarding mom and I being mistaken as a couple.   Some funny, some infuriating.

Mom had me at 19.  Dad was 21(they married at 17 and 19).  When we would get the nasty looks from older ladies and chuckles from older men mom would have been in her late 30s and early to mid 40s and I in my late teens and early to mid 20s.  I used to frequently and in an slightly louder than appropriate voice drop the "Mom" reference when I would notice the looks from people.   

My DW and SS get those same kind of looks now and have been getting them for years.  She is 43, he is 26. She was 16 when she had him.  They don't do anything odd. They walk arm in arm, he opens doors for her, etc....

She and I even get them now. I am 55, she is 43 and looks 10-15 years younger than her age. I have historically looked far younger than my age... but... time is taking care of that over the past few years.