What If?

Sometimes I sit and wonder "What if?".  Lately it's been about the choices that I've made in my life in regards to guys.  Right now, I'm stuck in a tough spot where I'm in love with one of my best friends but he feels as though he can't cross that line and become more than just friends.  Well, this is what has been told to me.  What I don't understand is if he feels the same why can't we act on it?  I've made this same mistake once before in my life and I ended up losing one of my best friends because we let others get in the way of our friendship.  I want to be able to tell this guy how much I do like him and how much I care for him but I don't know how.  It's really hard for me to let others in and I don't want to make the same mistakes that I made before.  Hopefully one day we realize what we mean to each other and things will be right.