You are learning a hard lesson, but it is good that you are learning it while you are so young. When someone has demonstrated selfishness and lying and breaks your heart, it’s generally not wise to go back for more. This young man isn’t ready to date anyone seriously. At 15, that’s not surprising. But nature is unkind in that young women are generally more ready to commit than boys of the same age. You invested far more in the relationship than he did.
High school dating is complicated and scary. My guess is that you keep thinking about this guy because you don’t really want to get back into the issues that go with being available and unattached. I con’t blame you a bit for that. But I do think this guy isn’t for you — or anyone else for that matter — until he grows up. Let it go. Take some time to be single. Work on developing your own interests and solid friendships. Remind yourself that you are lovable and interesting and that there is someone out there who will value you and cherish you when the timing is right.
I wish you well.