If my[18m] partner[18f] never wants sexual contact, then what are we?

We've been going for 4 years now. We experimented when we were first together and within about 6 months we were pleasuring each other and eventually we started having sex. She was on the contraceptive pill so having sex was quite easy and we have it regularly, 2-3 times a weekend (including friday night fun). It got to a point where she wasn't so interested in doing it, I understood that sometimes she was sore or just generally not in the mood.

Then she stopped taking the pill. For the next 6 months she wasn't interested in my sexually and was annoyed whenever I made a move. Now I appreciate her privacy etc but it was making me feel unwanted and realistically we were only seeing each other intimately at the weekends so I expect a little love for even half an hour when we could and even then, it wasn't going to be full on sex.

Then after a while she went back on the pill. We were both ready for sex again and I think both her and I were happy when we were having sex again. Jump a further year down the line and now its got to a point where she doesn't want to touch me. She doesn't like kissing nor snogging, and she especially hates it if I make a move on her. What do I do in a situation like this?

I love her to bits and I enjoy her company. We do other things like most normal relationships apart from anything sexual. I asked her once during an arguement, 'If you don't find me physically attractive/appealing, then what are we?' I'm not particularly overweight and the stress of exams and university hasn't helped in my beauty deparment.

What do I do?

TL;DR Concern boyfriend has oscillating sexual relationship with girlfriend and has to deal with gf not finding him sexually appealing anymore with the threat of a split