Hey,
I just want to let you know I was in that position once, where my best friend at the time started dating my ex. My ex and I were broken up for like 3 months, but it still hurt and felt weird seeing them together, just holding hands or kissing. I felt like I lost my best friend because of a guy because I was secretly hurt, but I did not tell her that. I think do what your heart says. My friend did, and she picked the guy! I was lost, but I started hanging around other people, and got a new boyfriend, which ended up being my ex's friend. Weird! Anyhow, your friend could have loved your boyfriend, but they just didn't get along much. But, I still think go with your heart. I think you and your best friend need to talk this out because losing a friend is not fun, especially your best friend. Maybe she is just uncomfortable seeing you two holding hands, hugging, kissing...like me. Try to work this friendship out, but if you really love your boyfriend, don't let it ruin that relationship. REMEMBER: it takes two to make a relationship work...if your friend doesn't put here forth towards the relationship, maybe she is not a true friend. Think about it.
This is a sticky situation, there is no right and wrong to it.
Hope it helped,
Pam