Immature teenage relationship question (details inside)

So… there’s this guy (let’s call him Jason). We’ve been together for a year and a half (I know that’s not much, but when you’re 16 it really is a long time) and for the first 10 months it was all so awesome, crazy teen love etc. But now he’s all mean to me, won’t kiss me, we haven’t had sex in about a month, we already have broken up once (but made up in a couple of days, mostly because I missed him and went to his place to talk to him) and now it’s more like we are cousins, not a couple. He’s always in a bad mood, doesn’t talk much and won’t ever tell me what the hell is wrong. And when he does talk to me, he either complains about his parents or tries to tell me what to do (which makes me sooooo angry). I used to be the one who does everything possible to keep things alright, but it’s been so long since I last felt it’s worth it. I think that I just don’t have the guts to break up with him, I’m still there because of how we used to be, and because he “is a nice guy” when he doesn’t beat his brother’s dog and when he doesn’t make me miserable. He used to mean so much to me, and I have this stupid tendency to forgive him even though he rarely says “I’m sorry”, ugh… am I being as stupid as I think?
And I already have very strong feelings for someone else, but I can’t really have him so I stay with “Jason” because that’s the “easier” thing to do… but it’s horrible, I am there with him and in my mind, there’s the other guy and things are already messed up enough. I’m so confused, sick of this situation.

Tell me what you think, anything. Any advice?