How and when should I break with him?

I think you should be honest with him and tell him the real reason why you are breaking up with him. And you should do it before the New Year. You could also tell him that you find that 15 is still too young to be in a serious relationship. You don't need to feel bad because you don't have any feelings for this guy. And you should not force you to stay with him. Your friends telling you that you should stay with him because he's sweet and caring is really unfair because they are not the one who has to endure him. If you don't break up with him before the 31st then he's going to be furious with you that you went to the party on the 31st knowing that you were going to break up with him. That is why I say break up with him before the 31st.