For a period of time in my last relationship, I was on medication that totally killed my sex drive. I felt really bad about it (and endured no small amount of guilt-tripping from my then-boyfriend), but I just couldn't seem to WANT sex, and when I gave it a shot anyway, I just couldn't get physically aroused, and even with lube, intercourse was uncomfortable and unpleasant for me.
Is he taking any medications? Or have you noticed any other changes in his mood or behaviour? Sometimes things like depression can kill a person's sex drive. As someone else mentioned, it might not be a bad idea to talk to a medical professional, just to rule out any possible physical, psychiatric, or homornal issues that could be at play, because those issues are more common than many people realise.
I'd also say it's time to sit him down and have a serious talk. Make it clear that you don't want to make him feel bad, but your needs are not being met, and that needs to be addressed. Make it clear that it's not enough for him to just reassure you that he still loves you and then nothing changes; that this is something the two of you need to explore and hash out and get to the bottom of. You don't have to make him feel bad about it or be mean about it, but you shouldn't allow him to brush off your concerns, either.
Maybe sex has just become boring and routine by this point in the relationship? If that's the case, it's an easy enough fix. The two of you can talk about fantasies you might have, or new things you'd be interested in trying. You can try introducing things like toys or restraints or roleplaying or whatever else of a million other things might appeal to both of you. Relationships take work, especially after the excitement and newness wears off. Sometimes it's easy to forget that, and just assume that so long as you love each other, everything will work out fine (I get the impression this is the attitude your boyfriend has, but I could be wrong)....but that's not really how people work. It takes effort to keep things fresh and exciting, and without that effort, it's very easy for things to become stale, no matter how much you love each other. And remember, if you need inspiration, the internet is a wealth of information on sex and kink, haha (hey, this site is a good place to start!).
Whatever happens, I wish you the best of luck!
