When you two first got together, you were only 14 1/2 and he was 17 1/2. At those ages, he was an older and maybe wiser guy who could be someone for you to lean on. It may be it was kind of flattering to him to be needed so much. Now he is in his twenties. It sounds to me like he is feeling torn between some loyalty to you and wanting to explore what it means to be young and single. He may be ready to give up being the strong one in favor of finding a relationship that is more equal. You’re hanging on as much from dependency as from love – which is never the basis of a healthy relationship.
What you do at this point is start to deal with the underlying problems that have left you so alone. Appreciate your teenaged romance for the good thing it was and let go. A relationship that is so one-sided and built on caretaking is not one that will last. You need to take over the “fixing” and learn how to take care of yourself. Find a counselor if you can. If you feel helpless about how to find and keep friends, group therapy is often a really good place to start. Take advantage of any opportunities for growth that come your way. Develop yourself so that you have a whole, healthy person to bring to the next relationship.
If you need someone to talk to while you look for a counselor, you can call the Boys and Girls Town Hotline at 800 448 3000. There are counselors available there 24/7 for young people like you to talk to. Check out their website at: http://www.boystown.org/national-hotline.
I wish you well.