How can I start a relationship??

Being gay has nothing to do with the answers to these questions. You'll know the same way you know whether anyone likes you: He is interested in who you are, not just doing sexual things or exploiting you in some way. He enjoys being in your company and lets you know that, both verbally and nonverbally. He asks questions to learn more about you and doesn't just talk about himself, and at the same time isn't evasive about answering your questions about him. You've had friends, probably good friends, since early childhood. A possible romantic interest should start out as someone with whom you think you could be friends. How you'll know if it's more than that? Give it time. Don't expect to know on your first date. The idea of a first date is to see if you both want a second. The idea of a second date is to see if you want a third. At some point--you will know without anyone telling you--one or both of you will reach a point of decision that you like this person more and differently than you've ever liked any other friend, or that you're finding yourself feeling, deep down, that even though there might be a little something there, you're wasting your time. Bottom line: First date does not equal boyfriend. Don't allow your desire to have one make you assume this is the one. Find out for real just by listening to your feelings honestly.
Best of luck. This is a good question.

If you haven't even met this guy in person you can't very well say he's your boyfriend. That (somewhat meaningless) title is something that comes later after you've been dating for a while and have discussed whether or not to be exclusive.