You actually can't blame SD.  DH is allowing it SD is going along with it. Happily going along .  If DH put her in her place, this would not be happening .   Y our mi stake was not to. Stop this nonsense  20 something years ago.  Or became fed up and left 

I can sympathise because I have two SDs who behave in a similar fashion.  SD29 is by far the worst, and after an episode in Spring 2022, I cut off all contact with her and DH now sees her away from our home.  DH reacted badly to this at first but now seems to have come to terms with the fact that I refuse to see her.  Unfortunately, for both you and me, this is largely a DH problem as he is allowing his vile daughter to treat you in an ultra rude way - I know that if my own daughters treated DH the way he has allowed his daughter to treat me, I would be down on them like a ton of bricks!  

I still feel rage at the way SD29 treated me 2 yrs ago, but it is good that I don't have to see her any more.  My DH does acknowledge that she is a difficult person - whereas it sounds like your DH promotes it and is OK with the fact that your SD excludes you from conversations.  Really, I would suggest that you and DH have some couple counselling about this, preferably with a counsellor with step family experience.  

It feels like another woman in his life because it is. Their relationship isn't normal or healthy. A 27-year-old woman should be mostly busy with her own life, not scheming to break her father and his wife up or sabotage their relationship. 

Welcome to the club nobody wants to be in. I was also the other woman whenever SD was around or had orders for her father.

I spent too much time (and money) trying to be nice, understanding, patient. But eventually I had enough. I had a major meltdown and DH had to either treat me as a full-time spouse or he could continue to jump to SD's commands.

The more he tried to have a normal relationship with her, the more she ramped up. A few years ago he did or said something that upset her, so she cut off contact. Won't even tell him why. He is deeply hurt, and I suppose that is her punishment for him.

There is a sickness there. Maybe a bit of narcissism. I'm proud of DH for not groveling and begging for her attention, but I'm sorry for him too.

I would not tolerate either one of them. Time to bring the zero tolerance down on both of them like stink on the shit that they behave as.

Tell DH that you're done with her disrespect and his faciliting and tolerance of her shit behavior.

When her nasty mouth opens, shut it down by confronting her behavior then confront daddy for not shutting it down before you have to.

I agree with Kes. Perhaps even see a therapist yourself and then bring in DH. This situation is ridiculous and terribly unfair to you. 

My life is heading this way too a little bit, except DH seems to be waking up more and more these days, so that's a good thing. Agree that you shouldn't be tolerating it either, and agree that it is more of a DH problem. Your DH needs to wake up & smell the sh*t. Sending hugs, I completely understand. 

Now she's changed tactics on the odd occasion I have to see her she blanks me from conversation. Only choosing to talk to him about anything she can think of from her past that doesn’t include me, mainly the times she spent alone with daddy.

When she pulls this shit immediately interrupt and flood the conversation with all of amazing things that you and SO have done together.  Out play her at her own game.  Make the goal either her losing her shit in anger, or melting in tears.

The be direct with her and tell her that no more will her manipulations be tolerated and she can either engage in respectful interface or she will face an amplified version of what she does pushed back in her face

Over, and over, and over again.

KISS.

Do not tolerate unacceptable disrespectful behavior. Not at all.

Id go back in time and re-read the comments from your previous blogs. That always helps me gain perspective.

Therapy will help, dealing with the emotional outfall of all the toxic. Go for YOU. Take care of YOU.

She is 27... no need for you to hold his hand and wipe her nose... I would not socialize with her... and just be civil when you must be with her.. let him manage the relationship with his daughter.. you can be too busy to participate.

Its a love triangle you were thrown into and yes it feels like the other woman because it is. Its unhealthy its sick and creepy.

The only advice I have is to stay away from her. 

As much as you're enraged about his daughter and her behavior, it's really a DH issue.

Disengaging only helps so much, espeically when you feel like your marriage has a mistress in it. A triangulated relationship seldom works, unless both parties make a committment to MAKE IT WORK, which your DH has no interest in doing this. He seems to enjoy the circus he's created.

It's time to bring the big top down on your DH and rethink your relationship, and what you really want out of it.

I'm so sorry you have been fighting this battle, and not to sound hopeless, but it's a battle seldom conquered, because daddy's seldom standup for their marriage, but instead, side with their daughter wives.

I fought the battle long and hard for many years. Ultimately, it ended in a long, drawn out divorce filled with visceral hatred from his side and his daughter wife.  There are wonderful men out there who know how to value their marriages and prioritize their marriages. I found a great one.

You  may not be the the point of throwing in the towel, but if your situation is anything like mine was, and  it sure seems like it is, I can honestly tell you I was merely existing and not living. This earthly ife isn't a dress rehearsal, this is all we get.

I relate to this so much!  SD22 is more like a mistress on the side.  It feels like DH is having an affair.  I raised SD from age 4, yet now that she's an adult, she went to live with BM.  She has become an even darker cloud over our lives.  First, she estranged herself and went No Contact with any of us for 3 years.  DH was so distressed over her estrangement that he said and did anything to win her back.  She refuses to take his phone calls so their entire relationship is texting and DH sending her money.  He sends hundreds of dollars almost every month and tries to hide the bank transfers from me.  Ever since SD moved away from us, DH has hidden any news of her from me.  It has become a weird "love triangle."  I agree with "Miss Texas" that I want to leave him so bad.  He has never stood up for our marriage and doesn't put me first.  Ever.  But I'm 55+ and we have a 14 yr old BD and find it impossible to imagine a divorce right now.

Daddy's may lose their testicular fortitude to stand up for their partner an marriage.  Fortunately is not the case for my wife.  
 

She had clearly stipulated standards from day one that I am her husband and I am also an equity parent to her son... er, my son.  I would have tolerated nothing less even if she felt otherwise.

Heaven protect SS, the SpermClan, or my IL's if they tried to discount my standing and the standing of our marriage.  The carnage she would bring to bear on any and all who made that mistake frightens even me.

Some of those same people did make the mistake of discounting my bride and immediately were dealt with by me, much to their pain and chagrin.

We never had any of this to deal with in our relationships with my family.  For some reason the SpermClan and even my ILs  missed the "Don't F with us" memo.  I think it is the water in SpermClan that is the problem.

Though my brother an I were raised from the moment of conception never to test the preeminence of our parents relationship above all else including their children.  Our parents respect that model with our marriages  and we all have remained close.  With the exception of some years of drama driven by my SIL early in their marriage.

I'm sad for SParents with a ball-less mate who simpers after their failed family baggage.