I think I’m inlove with my best friend.

We have been friends for almost 5 years and I really don’t want to ruin anything, I know she doesn’t feel the same and I don’t know what to do. She had a boyfriend not too long ago which is the reason I realised I was inlove. I would get really jealous when they would show any kind of affection towards each other and I would always be wanting to touch or talk to her, she was and still is the only thing I think about.