I think it is fair to leave a relationship when it is not working out for you.
It's just that a child complicates things so much.

Also, I think it is only fair to tell your partner you are dissatisfied. I always feel the pain when I read a story about somehow who thought she/he was happily married where the other person just one day called it quits. Ideally, a relationship starts out perfectly, and you warn each other when it's not perfect anymore so you can both make it perfect again. Of course, this relationship was never perfect to begin with and the OP has already been honest with his wife.

The way the OP describes this it is something that is only going to get worse over time.

Is there anything more holding you two together than the child? If I ever had a child, I feel that I would almost feel as if my life, and my partner's life is over, and that everything is now about the child. So surely, that complicates things.

Most relationships are ended by woman, and they do it in a matter of days. And they have the full right to do as they feel.