IMO, your husband jumped at the opportunity to play innocent and put you in the role of the bad guy. He should not get a pass on this. He deliberately chose you throw you under the bus by saying NOTHING. 

It is never too late to disengage. If you plan to stay married to him, plan your own enjoyable activities with your friends and let him wallow in the stench of half-truths and lies and dysfunction with wretchedness of his own making. He should spend time with his rotten kids OUTSIDE OF YOUR HOME. Make your own plans. If you can summon up enough grace to attend one of their dysfunctional events, treat them like crappy coworkers: be polite, but distant. Rise above their BS with the gracious lady act. Read up on the Gray Rock method. 

These people have never appreciated. Don't let the opinion of low-grade people concern you. They're opinions are crap. 

"He told me he is "afraid she'll be mad at him and not want anything to do with him", so that is why he never confronted her on anything having to do with being nasty to me."

Jeez. He's still operating out of fear with a daughter who's pushing 50. Clearly there is deep dysfunction in THEIR relationship. Them. Not you.

"I'm now spending time with my wonderful group of friends as we do so many fun things together."

That is wonderful. It's the best response you can have to the sh!tshow you married into.

"After all these years of being put last, I just don't want to share with him.  Please be honest. Am I wrong to feel this way?"

Not even a little wrong. 

I would nail his wrinkly sack to the floor over this if I were you.

Start making your best life for you. Particularly when he is on his scent tracking of his adult spawn trips.  Post fun stuff you are doing.  Go to a spa and get the full meal deal package for the duration of his trip.  Meet with friends and do fun stuff and plaster it all over social media tagging him in it so he sees that you are very fully and in his face living well.  His spawn will know.

Relish in that.

I have zero tolerance or use for a mate that would sabotage their equity life partner over having their own issues with their own toxic kidult failed family spawn.

Character counts. He has none.

DH is also afraid of his adult kids. That drove most of his behavior and I was expected to smile and go along with whatever they decided. And pay for much of it too.

I reached my breaking point over a particular incident. He had to decide if I was his full-time partner or not, and if not, then we were done.

He started to "disobey" SD by keeping commitments to me and not running after her whenever she told him to jump. She was not happy and did eventually stop contact. So, essentially he did lose her. That was HER choice. But he could have handled it better too. The parent-child dysfunction is deep. 

DH still loves her, still contacts her to see if she's ready to talk, but she's rebuffed him now for three years.

I'm sorry for him, but I had to protect myself. 

I love that you have your group of friends. And, of course, no, you are not wrong to feel how you feel. I'd be tempted to pick up the phone, call SD and tell her the whole truth, tell her that I no longer give a $hit about her rudeness--that I let go of that a long time ago--and that it's her father who brings it up, adding that the two of them have "pathological" issues you want no part of.  

Keep enjoying and developing your own life with people who treat you right. Too bad your group of friends doesn't include some handsome, caring man! Yes, I said it! grrrrr. 

"He told me he is "afraid she'll be mad at him and not want anything to do with him", so that is why he never confronted her on anything having to do with being nasty to me."

This brings back memories of how DH handled OSD at the beginning of our relationship. Yes, he did stand up for me. He would end conversations in which she tried to drag me. He would tell her she needed to make things right, that I had done absolutely nothing wrong. Yet, she continued to drag me through the mud to him, those 'in family', and to anybody who would listen. He thought it would just get better. Experience told me that a one suffering from addiction and mental health issues and who had never been accountable for her wrongdoing was not going to stop. And she didn't.

The burning question I have is...Why on earth do they want someone like this in their life? Because they are family? (Likely.) Because they enjoy the drama and the pain it causes? (Not likely.) They have to make a choice. Are they going to continue to allow this stunted, dysfunctional individual to wreck havoc in their life? Or do they make a final stand and be prepared for the consequences? Or not make a stand and they lose their wife? Life is about choices.

Our life has been relatively peaceful once DH made a choice to prompt OSD to make a choice. She was given options and she was told the consequences of continuing her behavior. She not only continued her behavior, she doubled down. I truly believe she never thought he would stand firm, but he did. I know it hurts him. I also know that he now understands that he is partially to blame because of his permissive parenting. Sometimes our actions, or lack of action, bites us. Often the truth hurts.

Sad88, no, you are not wrong. You are right on track. Hold your groung. Blessings to you, I wish you satisfactory resolution.

DH is manipulated and controlled by SD's.  He is afraid that if he says anything and does not abide by what they say he will never see them or his grandchildren again.

They hate me and I know it.

It took a really long time to disengage but I think that I am finally there.  DH asks do you want to go to Gkids school, they are getting awards, no thank you.  I am inviting SD's and grandkids over, I say " that's nice, have a good time" and I do my own thing.  I no longer buy cards and gifts.  I am so over all of this.  It took well over 20 years to get to this point.  DH has the nerve to ask why.  He knows why and I am not discussing it with him again.  He's not going to change and they are not going to change and I am just so over it all.