Because:

1. You and DH are a couple, not Dh and ex wife. No playing "happy family" doing dinner and holidays together. That went away when marriage ended.

2. It is disrespectful to you and your DH. Do not let this happen it will set a bad precedence. It will expand and grow if not pruned off immediately.

3. Why in the he!! would DH want to spend bdays and holidays with ex???????????????? She is ex for a REASON.

What does your soon to be DH say about this? What did he do about this? He needs to say "no I will not do this, lets do something together without ex"

Read your other blogs. He doesnt back you up and allows them to continually disrespect you. Pays for everything. They tell lies about you and now this. Im sorry you are going through this!

No.

There is zero reason to play happy family. They know what "divorce" means--their parents are no longer together. It's WRONG to encourage the fantasy that these girls evidently have.

No. And it'd be a hill to die on for me, not a high road.

It's perpetuating a fantasy for his kids.

If they want that then invite you too.  Otherwise they can have separate dinner with BM and separate dinner with Dad.

After 5 years of divorce, all those life events should be celebrated separately. One birthday dinner with you and Dad and sister, and one with Mom and her SO and sister.  Graduation dinner, maybe everyone goes together, but that includes you.

But it's up to your DH to set that limit, and it sounds like he hasn't - so your issue is really with him.

Why is your SO still putting up with this shit? Why are you?

They are too old to be acting like this, which tells me that it will NEVER end. And, your SO will obviously not put an end to it.

Welcome to the rest of your life.

1. what will you do when he tells you he's going and you need to just get over it?

2. do you not see what's going on? They want you two to fight, if you stick around, their free ride might end. 

3. why do you want to marry this man?

Now, right now, is the time to squash this. If it isn't squashed now, you are setting the precedent that this is ok. If you let this go, you can look forward to years of exclusion. Birthdays of SDs and eventual grandchildren, weddings, graduation, holidays, etc. 

If my soon to be husband went to this, he'd find himself my ex soon to be husband. 

I'm surprised you are still with this guy, AND soon going to marry him. 

Look, no one can tell you how to run your life, but based on your other blog posts, you are signing up for years of heartache and angst. You had so much good advice from people here, people who KNOW what they are talking about, and who wish they could turn back the clock.

I think you're making a big mistake. This guy is weak, controlled by his daughters, and he definitely doesn't have your back.

#2.  Even if you don't particularly care about this event, you don't want to set the precedent of allowing the SDs to disrespect you and your relationship with their father.  No how, no way should he attend a birthday dinner with his ex wife unless you're there.  Ideally, he'd celebrate with his daughter separately, without the ex-wife.  She's an EX.  As much as the SDs may wish they were from an intact family, they're not.

If your soon-to-be husband is seriously considering this, I'd be reconsidering the marriage.  He should not allow you to be excluded and he should be standing up for you to his daughters.  If he's not doing that, you'll have a tough row to hoe.

Mom n dad back together.

My ex 23yo sks wanted this n always talked about their mother with him in front of me. He still was in contact with her. I felt he still loved his ex and if she ever wanted him he'd toss me to the side for her.

I didn't marry him to be a place marker or to come in 4th place after exw and his triplet adults. 

No. Just no. 

I'd be out the door if he ever considered any of this to be acceptable.

This is exactly how my DH became an EX! This exactly happened. DH took ex B wife and snotty SD out for snotfaces Bday. Read my blogs. I threw him out after that. It was years of torture and I had enough.

Guess what I have never been happier , they can all have eachother. Sick flucked up family. 

Dont be me. PLEASE.

He's making choices.  

You can either accept them or walk.

I'm telling ya, if it was me, and my man wanted to continue to play happy family with his Ex, I'd be trippin out.

You have a collection of excellent advice above!  Read it, understand it and heed the warnings!  I only allowed that to happen ONCE, when my manipulative YSD wanted to have lunch with her Dad, BM and herself.  I thought it was weird but I was young and stupid and I let it happen.  Thankfully, I let my instincts take over and it was the first and last time it ever happened, (but not for lack of my YSD trying for a repeat performance).  My DH, for the most part, takes my side when it comes to the Skids.  You'd better get him on board your train, or throw him off before he "derails" your relationship with this crazy behaviour!

If he perpetrates this crap with his failed first family... he needs to be your XH.

No way would my DH even agree to this kind of exclusion of me, and my stepkids wouldn't ask for it. Now I'm not saying they are crazy about me, I got one text for Mother's Day and nothing from the other one; but neither would try to set up these kinds of dinners.