Aw tigwig, sorry to hear you aren't pants-burningly horny!
I am 21, and tbh I feel pretty much the same, and it isn't my partner's fault. I am just not bothered. If I had to choose between sex and a cuddle, I know what I would rather! It's just a chore! I think if I didn't work or study, and I wasn't so exhausted, I wouldn't feel so negative.
I think Cinnabon is right, you need to have a good chat and some time alone. Don't know if you have kids, or other commitments, but maybe you could go out on a date every week, taking it in turns to pick where. Go back to basics-spend time getting to know one another's bodies again. It's easy to forget that sex is all about mutual enjoyment, and not about fitting it in between work and bedtime!
Toys might help, or dressing up. You could try exploring each others' fantasies? Just make sure that you are both honest, but tactful, so that neither of you feel inadequate or discarded. Lots of luck :)