Actions speak louder than words.  The first time I disengaged from my husband's adult son I just quit doing anything with him.  He did not live with us so it was fairly easy to just avoid him.  I didn't ask about him.  There was no big announcement - although like you I thought about it a lot.

Gradually SS33 cleaned up his act, and I started  being okay with his stopping by with his GF and their baby. Even had them over for dinner.  But after their HIDEOUS behavior 1 1/2 years ago I just said "Keep them away from me" to DH.  There was no way for DH to defend their actions (ransacking our home while we were on vacation, sleeping in our bed, etc.)

Now I do not bad mouth them. I don't make my DH listen to a stream of how awful they are.  I just said the "keep them away" phrase with such venom and hate that my DH knew I was DEAD serious about never letting them cross my path again.  I could go on and on for days about what horrible people they both are.  Their child (now 2 1/2) very likely has fetal alcohol syndrome - they are that disgusting.  But there is not one thing I could do to save that child.  But I do not say a word about them - good or bad.

My advice to you is to kick the bitch out of your mind.  I know - not easy.  But as of today she does not exist to you.  You can do this.  It's okay.  So she's getting married - give it no more thought than you would to a stranger getting married.

IF you are invited to any showers, etc just politely decline.  No elaborate excuses needed.  "I won't be able to make it."  And you don't even have to send her a gift.  You do not have to volunteer to do anything for her.  She will of course be more than willing to suck you dry of money and then treat you like the hired help who needs to sit at the back of the church or in a corner somewhere.

Stop thinking about all the horrible things she might do to you. You do not have to allow her to abuse you. She can't do a thing to you if you keep her away.  Sure she can say crud about you - but immediately stop anyone who tries to repeat it to you.

The wedding is two years away, I would not stress over it, right now, a lot can happen between now and then.

Don’t let her think she is better than you. You are better than her. You don’t have time for her.

You've got two years to plan a 2 week long European cruise with a good friend or family member for the exact date of the wedding.  Regretably you won't be able to attend but will send a set of Tupperware along with DH for the happy couple.  

Sandye gives great advice on disengaging and it's pretty much what I did.

"Do not show your hand to any of them. Simply say no to everything involving the step spawn."

I never announced my disengagement to DH or skids but just stepped way back and became very uninterested in skids and redirected all of that energy into myself and my marriage.  During the first 2 years of our marriage we talked and fought about skids often and now the subject rarely comes up and when it does I make sure it's short and sweet.  

I went through the same thing with an adult SD: cringing just hearing her name, anxiety every time I had to see her, my anger after every time I saw her, and the worst is that resentment you feel toward your husband.

You're on the right track with disengaging. Tell your husband you don't want to hear from her, hear about her or have anything to do with her because it's just too painful for you after all that has happened. He can see her alone outside your house. Tell him you don't want to get in the way of his relationship with her and this means less tension so he can enjoy his time with her -- it doesn't matter if he doesn't like her. It's just something he can't possibly argue against because YOU'RE DOING IT FOR THEM!!!!

If you disengage to this degree, the resentment gets better. You stop having daily arguments when a SD visit approaches. You don't lose endless hours thinking of SD's sins of the past because you aren't reopening that wound every time you have to see her. It gets better.

The wedding is way off. I doubt enough will change for you to want to be there. But if you press disengagement now, he will probably expect you won't attend...or at least he won't be surprised when you tell him you won't. If his ex will be there, all the more reason for you to stay home and not cause more friction -- YOU'RE DOING IT FOR THEM!!!!!! (Self preservation is a nice side effect of all this selflessness!)

I bent over backward for my SD's wedding, even after everything she'd done to me. She was very sweet in that year leading up to her wedding. I really thought we'd turned a corner. The wedding was uncomfortable, awkward, tense and miserable for me (and my husband). SMs are just there -- no one thanked me, no one included me, no one acknowledged the weird position I was in nor that I was sucking up so much to keep peace with BM and SD. I came home just happy I didn't end up with a black eye from the ex. Within six months, my SD was back to acting like I didn't exist.

On the plus side, I dropped 20 pounds from anxiety before that wedding and I didn't even have to try!

I have two adult skids, both mid twenties, both left home, I have been in their lives for 19 years, gave them everything i could give, I am the complete opportsite to their abusive preditory BF....they hate me....I can do no right by them, I love their Mum with all my heart...but I feel alone all the time, I just wanted a family, I got pain.  I am trying to stay out of sight so DW doesn't have get upset and choose sides.

Wow. Definitely one of the questions I myself need to ask. Don't feel alone. Sd is getting married next year and as this approaches I'm sure to see lots of drama. You're not alone at all

Many on this site helped me a little over a month ago when I was just married and my adult SDs sat through the wedding, adamantly pouting and glaring. Yes, that was hurtful, but here's the benefit: DH had to face the fact that they behaved outrageously. Never spoke to me, my children, my family, left the reception to stand outside, DH followed them (THAT isn't going to happen again). So many people at the wedding saw all of this and commented on it to us that DH can no longer pretned the "girls" (grown women) are just being misunderstood—not when his business friend says to him, "Hey, who were those sullen women in the front row?", not when my children say to us, "I tried to talk to your kids but they looked right through me." The up side is that he sees it all and that my decision to have nothing more to do with them is now unchallenged. He gets it. I hope your wedding goes better than that, but if I were you, I would not attend. 

Weddings, funerals, graduations feels like a trap from the first family. Its prime opportunity for a SM to be crushed, marginalized, shunned, and the list goes on. 

If your gut knows, stay far away. We are always worried about protecting DH's feelings that we arent there to support him. The problem with that no one is there to worry about ours. Mind you the wedding is 2 years away, plenty can change until then. Remember weddings can cause the worst bridezilla syndrome, so you can just imagine how rough a SD can become. Sounds like you are thinking ahead and already know the score.

I attended my SD wedding.  After contributing financially, emotionally I was clearly the outsider.  Out of the pictures, out of the thank you’s,  out of the family seating area.  Why set yourself up for this?  The cruise suggestion sounds good. Look after yourself,  when you see a train coming, get off the tracks.