just be friendly and talk to them its good to become friends before getting serious so you get to know them
You let him go or you keep him and tell him that "I want you to like me and not anyone else. Like boyfriend and girlfriend like".
You tell em u like em and if they still like da other person move on they dnt deserve u
What to do? Simple, look for another person you like. There is plenty of people. 6 billion humans. At least half are men or women. Deal with reality. There is no sense in wasting your time on...