Plz help me!!!

I'm going to be really straight forward. I am not happy with my boyfriend...He is constantly texting me in the middle of classes and always insisting on making out when I don't want to. He wants to hug me and kiss me and be all over me non stop. He's just to nice of a person to say "Hey I'm breaking up with you k bye." Oh and one more thing I'm a little bit more than halfway through 8th grade and we've been dating since the beginning of 7th grade which is a pretty long time but anyways he's already talking about sex and marriage and having kids.I'm not exactly the kind of person to care about that stuff rn...like let me get through school and college and then I'll talk about that. Plz give me advice on how to let him down gently. I've tried before and he used depression as an excuse to get me back and I feel like I'm on a guilt trip bc I'm lying to him... telling him I'm happy with him and not upset...Plz I need help!!!