The ex πŸ‘ΉπŸ˜”

So I've been with my bf for almost a year and this days I started feeling so upset because of his ex. They broke up like two years ago but were together like 1 year and a half. The problem is that she keeps talking and going out a lot with my bf's younger sister. I don't really talk to her(my bf's sister) Β much because I'm a little bit more shy.Β 
And now I just found out that she still talks with his mother and sometimes they all 3 go out. I'm sure my bf is totally over her and I'm not usually insecure about myself, but I can't help felling jealous and upset.
He even told me that he hates that they still talk because he thinks it's time for her to move on.Β 
And also many of his aunts and cousin still talk to her a lot. And I can't help feeling that I'm doing something wrong for not having that kind of relationship with them 😭 my bf told me that I shouldn't worry because he never felt what he feels for me for anyone else, he keeps telling me things like I'm the one he's going to marry and things like that but
I don't know what to do, and I feel so sad πŸ˜”πŸ˜”I keep comparing myself with her and I hate that.Β