Search Results: found my dream girl

My SO has this best friend, who is a girl. She's nice and all, I guess, although I don't really talk to her as much. She also has her own boyfriend, so on the surface I shouldn't worry, right? However, I do remember that, before my boyfriend and I got together, she used to say that she had a crush on my SO (even while she was/is in a relationship). She doesn't say it anymore, I guess to respect our boundaries, but she has brought up a few things from the past, like telling our mutual friends about the time she told him she had a crush on him, how she played a certain video game for hours so her character could marry his ("my dream has come true," I remember her saying at the time), etc. Whenever my boyfriend is online (we're long distance atm), she shows up online as well.

Now, I trust my boyfriend, but I'll admit I get insecure. Thing is that my past relationship broke apart because I found out my ex was cheating on me with his best friend, who was married. My boyfriend doesn't flirt with this girl, but he often doesn't reply to my messages for quite awhile when *she* is online. Right now, I'm waiting for him to message me back--about forty minutes later. Yesterday he admitted that sometimes he forgets to message me back because he "absentmindedly" thinks he had already replied to me.

Anyway, I'm sorry about my jealous rants. I don't know what to do here. Should I bring it up with him and ask him why he ignores me?

But the main question is, how would you feel if your SO had a best friend of the opposite sex? What would you do if you were in my situation?