Having been the wife on the other end of this kind of dynamic, I'll share with you how I felt.

My then-husband worked while I stayed home with two small children. His job was very stressful, I understood this and catered to his need for validation, but I never got the feeling he appreciated how stressful it was to care for kids all day. In his mind, I got to "stay home with kids [and] all that crap." In return for my child-raising efforts, I got a roof over my head and food in the fridge, but also was treated as if I sat around all day doing nothing. My kids are (mostly) self-sufficient now and that "crap" is STILL exhausting.

When he was home, my then-husband would occasionally break himself away from his computer or busy-work to help with the kids or clean the house. For these times, I was grateful. At first. When I came to realize that sex was expected as a reward, that I "owed" it to him, I felt used and resentful. It made sex a transaction, not about a mutual... anything.

I don't think he helped because he wanted sex - I think that part was genuine - but when I was too tired or not in the mood, his reaction was very similar to yours. "I did [x] for you. You can't even give me some kisses or maybe play with it a little?"

Sex is very important in a marriage. The fastest way to turn sex into grudge match is to do what you're doing now. Instead, love her and take care of her. Help more often without the hope of reciprocation. Realize that staying at home with kids is very isolating and not as easy as you think.

All that said, I could have been a better wife. I could have been more proactive. I let resentment eat me up. I don't know your wife, but I bet she's feeling some of the same things. Therapy did wonders for me, though it came a bit too late. The two of you need to acknowledge and work on your situation together - therapy could do wonders for you yet.