AITA for refusing to be friends with my boyfriends F best friend

A little background; I (28f) have been dating my boyfriend (22m) for about 6 months. We met through a mutual friend and just kinda hit things off really well and started dating a few weeks later. We have had small issues as far as relationships go. Typically we only get one or two days to see each other a week because we don’t live in the same town and our work schedules are different. With this I haven’t met many of his friends and he’s only met a couple of mine, as well as some of my coworkers.

His F bestfriend lives about 4 hours away from him but they talk daily. I’ve been fine with this because I have male friends that I talk to daily, mostly my coworkers as I work with mostly men. When we first started dating he told me that he had a F friend we’ll call her Betty, that he did a lot for and would always be friends with. But also explained to me that they had a sexual relationship in the past. But they are only friends.

There have been times that I’ve been uncomfortable with the idea of their friendship just knowing that they were romantically involved at one point. But I let that go. We had one small argument over friends of the opposite sex where I got angry and told him “at least I haven’t slept with my friends.” It didn’t take him long to realize that I was talking about Betty. He said he would be taking a step back from how much they talk because it made me uncomfortable.

After this I figured it would be the end of the conversation for a while, but about once a week Betty is still brought up in conversation. At this time I just listen to him talk and will typically get off the phone or change the conversation. But last night he was talking about her and said to me “it’s too bad you don’t like her I think y’all would get along.” And how things were going to be hard for him with me not liking her.

Now keep in mind that I have never met Betty in person, or talked to her. So I don’t dislike her as a person, I just am not comfortable with the dynamic of their relationship. So AITA for not wanting to be friends with her?