Am I wrong or just insecure?

I think that you should sit down and have a good talk with your boyfriend. Explain to him all the feelings you are feeling. If he is a good boyfriend and most of all if you two are friends he will try to understand. I always say that a good relationship is based on a good friendship. The best relationships are built on communication. You need to be able to talk about what is bothering you without worrying about him being upset. If he can tell you that he cares for you and no one else and he has given you no reason to doubt him, then purhaps you can let it go. Maybe they are just friends and she is there visiting his sister. The other thing is maybe you should go visit him when she is there and see how he acts around her. I have a lot of male friends and that is all we are is just friends.

I think you might be partly insecure, but it could also be that you sense that he might be attracted to her and that might be the fuel to your insecurity. As with any relationship trust is the key factor. If you can't trust someone you are involved with then what is the point. If you trust him and he happens to betray your trust- then guess what that is on him, not on you. Maybe you should try to spend more time with your man too and meet this friend so that you can really find out what she is all about. The fact that she is his sister's best friend may mean that they have known each other for years. He may actually think of her like a little sister. Don't go over the deep end and get yourself worked up until you have had a fair chance to survey the situaton.