My boyfriend and I have been together for four years now. We've talked of getting married and are very affectionate with one another, and I care for him quite a bit. Something that I don't quite understand, however, is his lack of interest in sex. He's never been the type of guy to look at other women, and has never cheated on me. He's extremely loyal, as am I. But, strangely, he has no interest in sex whatsoever. He doesn't watch porn, doesn't masturbate, and only has sex when I initiate it and after some coaxing. I haven't changed physically at all in the past four years; if anything, I've gotten in better shape and learned to make myself look better.
He is 21, and I am 20.
In the beginning of our relationship, he was moderately interested in sex, but any ambition he had has almost completely disappeared. He claims that he just has a low sex drive, which I didn't think was possible until I met him. I'm one-hundred percent positive he isn't cheating on me, so I'm not worried about that. Is there any way to motivate him?
I've tried talking to him about it, but I always feel guilty when I bring it up. He's very loving and treats me extremely well. He always takes time out of his schedule for me whenever I ask, buys me almost anything I want, and does anything for me. He loves me quite a bit, and is always very cuddly and affectionate, and always wants to be touching and clingy, which I like, but sexually there's nothing. I feel bad bringing it up though, because it seems to hurt his feelings, and he's said things along the lines of 'But I love you, I'm loyal to you, and I do anything you want me to. Shouldn't love be significantly more important in a relationship than sex?'
Is there anything I can do to improve his libido without mentioning it to him?

This is kind of an odd situation! Usually it's the other way around... Anyway, if you plan on marrying this man, talking about his libido is going to be one of the least strenuous things you'll ever have to discuss.

Sex is a very important part of a relationship and it seems odd to me that he's guilt tripping you out of it. Instead of going behind his back and spiking his punch with animal aphrodisiacs, say to him, "I know you love me and I appreciate your loyalty and slavish attention, but I'm human and need a reciprocated sexual relationship." Ask him what turns him on and try it! Be unexpected and sexy. He might be in a rut and not know how to talk about it.

Also, it's strange he separates 'love' and 'sex'. In a meaningful and long-lasting relationship, sex is a way of showing love and he must not be feeling it. If he's seeing it as just a bodily function as a opposed to a physical expression of undying affection, he might need a little one-on-one with you. Explain to him that you don't want sex to be tedious or a chore, but a way to love him. Ask him why he doesn't see it like that. I think once you get some answers to those questions you'll be able to start rekindling that flame.

You were only 15 or 16 when you started going with him... you and he are just kids, and may be stuck in this comfortable relationship and afraid to move on. Getting more experience in life may scare each of you.

The sex thing is not going to get any better, in my opinion. He's *only 21*, and not interested.

Have a cordial but sad break up and move out into life. :)