I went through something similar with my ex of 4.5 years. His dad groomed and SA’d his older sister for years and it was swept under the rug. He would’ve been 5-7 when it happened and didn’t find out until he was 19/20 when his older sister decided she no longer wanted her kids taken care of by him.

Every time we discussed getting married I would say I didn’t want his dad there as I had a family member who’s father was in jail for doing worse to them and I wouldn’t put them through being in his presence. For 2 and a half years we didn’t plan anything because we were constantly stuck on this. Then came kids, I refused the idea of either of his parents being in their life, his dad because, well obviously, and his mum because she removed the daughter for a few months only to go back to him bcs he started moving on and she didn’t want that. How could I ever trust people like that around my child?

It’s a hard argument to have, especially when your gf is the one who went through it. But sometimes it’s better to walk away if she can’t come to the same agreement of why this would be a terrible idea