My (24F) boyfriend (28M) has a female bestfriend that's had a crush on him for years. She has been in and out of his life multiple times as she confessed how she felt and they attempted a relationship, but he didn't like it nor want to continue pursuing it, which took a toll on their friendship after they had ended it. In a way, he was guilt-tripped into attempting a relationship with her. He said he wouldn't go for her again if she tried and their friendship is going to change entirely if they ever fix things. He hasn't spoken to her for almost 2 years because he couldn't stand how passive aggressive she started becoming, which was the case for an entire year. She came back into his life recently and I managed to find out that she still loves him and is willing to wait for him and would 100% attempt another relationship with him. Him and I argued about this which caused us to temporarily get a break. In the argument he said I should've never been concerned, that she comes off as being a little obsessed sometimes, and that he would still never go for her even if him and I parted ways. Should I be concerned about her advancing on him again in my absence? And do guys generally change their minds about this kind of thing?

I generally don't know how I feel about him having her around, given the history and the fact that she still loves him the same.

I can provide more context.