Well if he doesn't like you back, then it doesn't seem logical to go after him. Once someone doesn't like you, it's pretty hard to get them to like you. Only in stories does it seem easy but in real life, that isn't the case. You're only going to be wasting your energy if you try to go after him or make him like you. So my advice is to wait until someone who does like you back come around because I'm sure there is someone out there for everyone but you can't always know when.