Unhappy in relationship?

Ok, it's a little bit hard to ask this question on Y, but I really don't have anyone else to talk to. Please don't be judgmental. I've been in a relationship with this guy for nearly 4 years. He proposed to me last summer. I was really excited about it, but things have been going downhill since then. Granted Im in school and it's very stressful, but I'm really unhappy in my relationship. I don't like having with him at all. I find that he goes too soon and that it's not affecting me at all. I don't feel anything from it. Each and every time we do it and he goes too soon, he's always apologizing to me and saying "oh, I will do better next time". I'm just tired of always getting into something, and in the end, I become disappointed with it. I get easily annoyed with the things he does, and find my self constantly getting into arguments or yelling at him. I'm just feeling really depressed. I've tried talking to him about it, and he is very honest and sincere about the whole ordeal, and asks me what he can do to make things better, but I'm at a lost of what to say to him. He's previously had other ual partners before me and I've technically only been with him. I know he really loves me and I do love and care for him, but just not in the ual way. It almost seems like the spark we had when we first met is gone. He tells me he wants me all the time, but I feel nothing like that for him. Sometimes, I just get totally disgusted with the very idea of it. I see other couples and it just makes me frustrated that my relationship is nothing like that. I feel like I'm just playing the role as a fiance-soon-to-be better homes and gardens housewife, but nothing more. I don't know what else to do. I would really appreciate your thoughts, but please don't be judgmental. I'm already handling enough heartache as it is. I really don't want to lose him because he's treated me so well, but I'm at a loss of what to do.