His ex thinks she's part of his family

So I've been with my current bf for right at a year now. He had dated this girl before me for about 2 or 3 months and then broke up with her and met me a few weeks later. They were only together a short time and he broke up with her because they didn't really get along at all. Well she got incredibly close to a few of his family members (sisters) and has kept in touch with them. She also has tried several times to get back in touch with my bf but he has blocked her through every means possible. She is still Facebook friends with some of his family members, but really truly is only friends with one sister. The rest of the family she hasn't seen in a year. So recently, she invited his entire family over for a party at her house. His family told my bf that she also invited him, knowing full well that I exist and her been dating me for the last year. I feel like this is kind of insane. She was never part of their family. She is friends with ONE of his sister's, everyone else is just a friendly acquaintance. I feel like this is not how a normal person would act at all. They were together for only about 2 months. I think she's just trying to get back in contact with him. I really think she needs to let it go! I'm slightly upset about the whole thing, but then I kinda wish he would go, since he was invited, and take me along so I could say my peace. Ugh! Anyone else feel like this is just strange behavior??? I mean, I was married before for 3 years and I'm still on good terms with the ex in-laws, but she dated him for TWO MONTHS.

**Edit: obviously he's not going and neither am I, he has no interest in being there or giving her what she wants. But I'm still mad about the lengths she's willing to go to in order to have some sort of contact with him.