I hate being an avoidant. I constantly reject the love I crave.

Me (F16) and my bf (M17) have been dating for 4 months but ive known him for more then a year, he's absolutely amazing, sure he can forget things at times but hes always reassuring me, he listens to me and always saying how he loves me and wants to spend the rest of his life with me. Everything I've ever wanted in life. Yet for some reason it feels like it's to good to be true, I'm constantly pushing him away and I always feel bad for it, yet he says the right things always and I'm back to being happy like a love struck fool. I've never been like this with any guy I've dated and I'm scared. He says he wants to grow old together, and here I am barley pushing to live just one more day. He's so good that I'm scared that I might be harming him with my negativity. Even though I hardly say anything due to being scared of being annoying. He's so bright and here I am all gloomy. Why can't he see that? I just want the best for him really. I don't know if I should leave him, or stay and try to get better mentally..