He wants the ex-wife to attend...

Knottie

I think that your feelings are normal and valid to have. I did not date people with kids purposefully after a bad experience because I didn't want to have to deal with the necessary relationship they need to maintain with their exes indefintely and not having an ability to coparent children in my home.

So you've entered the relationship knowing this and accepting this. I'm curious to know how long you've been with your FI and living with him and dealing with his ex and how recently you've realized some thing were uncomfortable for you?

I say this because sometimes it takes a while to understand your position on a topic. In my marriage, I lived with my ex for 3 years before marriage and he was always the same way as I met him (very selfish and lazy) and I accepted it, but it took me over 4 years of our relationship together (after we finally married) to realize and be able to articulate how unhappy I was and that I didn't want to continue in that path.

I think this is the time to sit down with yourself and think about the fact that his ex will be most prominently in your life for the next 5 or 6 years, understand the positive relationship he has to have with her as a coparent, and understand the benefit of him having a friendship with her... and decide what things you realize you're going to have to accept on a deeper level and what is unacceptable to you beyond that...and bring it up to FI.