What are the chances of this relationship lasting?

if you think it's going to last then it probably will. and from the way it sounds, you two are really open with each other, so it's not like you're going to have any drama that involves communication issues or cheating. when he has the chance to go to college, that's when it's probably going to get tough, because that's basically when your life starts. it all depends on how much you're willing to sacrifice and go through.