You’re asking for a lot. In fact, it would be easier if you faced reality and understood that you have a mad crush on this guy friend and he’s not interested in you. The best thing for you would be to move on and find a best friend who’s a woman and not a man. His girlfriend or whoever his future wife is, is going to pick up your mad crush on her boyfriend or husband and not want you around — and frankly, she’d be within her relationship rights to want you out. In addition to which, you’re going to have a hard time finding a man in your own life as long as you harbor a fantasy that he’ll one day change his mind and want you as more than a sisterly friend.
My advice to you is wake up, smell the coffee, and do what’s best for you — which is to stop spending so much time with him, find a female best friend, and start dating men so you can find Mr. Right and not hoping Mr. Wrong is going to come to his senses — he already has.
Sorry! Sometimes the truth is tough to take.