Well, I guess you have guts, I'll give you that.
There's two sides to your coin.
I agree with everyone else, you guys don't sound like a good fit. Now, I'm not siding with you, saying that you're right. Or, wrong for that matter. Sex is a part of marriage for most people (I say most because there are some a-sexuals out there, and everything is hormonal), so I'm not too surprised he wants it that often. And he may want it a lot more often than 'normal', but you're lucky he wants it at all, being as sick as he seems to be. That just tells me he's on the mend, or taking the chemo well. Young love is what it is. And being what it is, you guys should have discussed these things or been together long enough before getting married to know that about each other.
On the other side of the coin, my husband and I, we've had our problems, some of which everyone thought we wouldn't be able to move on from. But, we have. And as hard as it's been, we're both very grateful for it. We could have split up 1,000 times in the past, but haven't and we mean more and more to each other every day. Marriage isn't easy, it'll never be easy - it's a lifelong decision and commitment. At least that's what it's cultural meaning and representation has been in recent history, and I'm assuming that's how you guys took it when you walked down the isle and said "for better, or for worse." Think of the ups and downs in a lifetime. If you split up, don't kid yourself. It's because you guys gave up. That's all there is to it. You guys, if you really want it to work out, and you really do love him as you say, you need to find the center. You need to come to an agreement, a compromise. If two people are willing to work at it, it'll work. If one of you guys is out, well what can you say. You just get back what you put in. When you first fall in love, you just receive, and giving is so easy. Later, it gets harder. You have to give and take, I get needing a balance. But in my experience, it fluctuates. I can't imagine how much it must fluctuate for you, it sounds like you're giving so much already. I get it. You may need more time to yourself, you may also be finding it difficult to be attracted to him right now, being his caretaker, watching his BMs, etc. You need to talk to him about that, and tell him that he needs to hear you out, and you guys need to work on it if he wants to stay together. It's completely possible. And like I said, being a caretaker IS hard. But you know what? I had no problem doing it. And if I could, I would have done it for the rest of my life. I WISH I could have continued. I would literally do ANYTHING, A-N-Y-T-H-I-N-G to continue, to have that. Just that little bit. You don't know what you have, until it's gone and smarter words have not been said. If you truly love him, appreciate every second. No matter how good the prognosis. And I realize how stupid that is a thing to say.
Ultimately, this is a question you guys need to talk about yourself, not ask a forum of strangers. It helps getting other people's opinions, especially from objective people, but in this case, I would say you probably just want to hear someone else tell you that your opinion matters. You're a human being. your opinion only matters to yourself. It's harsh, but that's how it is. Your loved ones care, but honestly it's probably mostly just you. Talk to him. That's all there is to say.