What should i do? Help please!?

I've liked this guy for pretty much 9 months. We're both 15. We had a thing for 5 months, which ended because I started to have a thing with another guy, which I really regret. The guy I like I'm pretty sure has moved on and we don't talk anymore. I know this sounds stupid because I'm only 15, but I honesty have never felt this way about anyone I have ever met and whever I think about him it makes me so so so sad, and hes the only thing on my mind. What should I do?