No my dear, you are not asking too much. Cancer doesn't impact only the patient - it tortures everyone who loves them. Unfortunately, as the patient, this is sometimes difficult to see. And it's understandable. There is so much fear that comes with cancer - it's just so much to deal with.
My husband was not himself either during his chemotherapy. We've been together 33 years, so I wouldn't say he was distant, but there were certainly times where he was not himself and my feelings were not top of mind for him. I certainly had moments where I felt cast aside, just like you said. Looking back I can see that it wasn't so much from his behavior I felt that - but from my own fear and need to reassurance. In the midst of chemotherapy, he was understandably not in a position to reassure me.
Please know that what your boyfriend is doing and how he is reacting - it is SO not about his feelings for you. He doesn't understand the fear and sadness you are feeling for him. I think a patient thinks that a caregiver is the lucky one. (They're NOT by the way, but it's an understandable emotional reaction.) Just continue to be there for him, when it's appropriate gently remind him that you are afraid and what you need from him (and I do mean gently), and always, always remember that the fear and the feeling like CRAP from chemotheraphy makes a normally giving, thoughtful and caring person turn into someone that you may not recognize. It's ok. That's what the beast C does.
In the meantime, take care of yourself. Your feelings are important too and don't ever feel bad for thinking so. And it is extremely important for his healing that he remain positive, that his environment remain positive, and that he stay focused on getting well.
And you know - I've found that cancer is hard for guys to talk about. I have a friend who's boyfriend had colon cancer - just finished a year's worth of treatment at only 33. This guy was angry, pushing her away, refusing to talk about it, all that stuff. It was hard for her but I just kept reminding her that's his way to cope. Not talking about it - typical male way to cope. Maybe he needs to feel like his life is normal - you know what I mean? Cancer just consumes everything. And in a normal life, we aren't communicating about cancer. I don't get it myself - but I think it's a guy thing.
I wish you both the very best ~ GDW