Honestly, I have those little insecurities too; I'm sure all girls have them someway somehow under some kind of circumstances. From what you've said, I don't think you need to worry. Why can't they be friends? I'm sure it'd be okay, as long as they don't re-kindle their old relationship from years ago. I think it's more of how they treat each other as friends that would need to have you worrying. If they're a bit too flirtatious then something would be fishy. But if they're just going to be casual friends who stay updated on each other's lives, it should be fine. I'm afraid of my boyfriend's ex coming back, but do what I do and try to put that feeling aside. If you don't, it's going to harm your relationship with your boyfriend. Just trust him, and don't grow any hostile feelings against his ex. Who knows, you two might become great friends one day. =)