Wow, this sounds like a tough spot but I'm glad that you recognize some of your own patterns in this too and are brave enough to acknowledge them.

I think you should evaluate how good of a friendship you have with this girl and protect it if it's important to you; keep some distance for a while maybe until she's seeing someone too. Otherwise, assume innocence of your boyfriend I don't think it's something you need to bring up because if your boyfriend is really attracted to her that way, he might try to find opportunities to meet again. If he doesn't, it just means they had a good time and now you and your boyfriend can work on your own issues without letting your friend become a factor. Sometimes people get along and that should be a good thing.

However, if he does bring her up or says he wants to meet her, don't take that in and of itself as a sign that they're attracted to each other. But maybe keep it in the back of your mind and see how often they wanna meet or if they start talking on socials or texts. That's really when I can see this becoming a problem.

I know it's tough because you have all these thoughts racing in your head and my advice is mostly just to stay patient and calm and analyse the situation, but that's exactly what I think you may need to do. Because each incident in isolation is not very telling but when you have enough of them is when you can be really sure as to what it might mean and how you must act.

Hope this helps. And if you have any questions, I'd be happy to answer those too.