While I don't feel that way about my own kids, as a father of three, I can certainly relate to that feeling. Men and women are wired differently, and we fathers often don't have the same emotions towards our children as their mothers do.

You aren't a monster or horrible person for having those feelings. I'd bet good money a lot of men have had to deal with feeling the same way. The fact that you're writing about it, and you have made the decision to not abandon your son, shows you aren't heartless and callous. But if you're willing, you have some work to do.

Two suggestions:

1) Find a good therapist. While I don't know you, what you've shared here seems to be rooted in pain not yet worked through. But go to therapy for yourself, not your son. It's to help you be better for you.

2) In the same way you've chosen to not abandon your son, try to also choose to like him even if the feeling isn't there. Force yourself to be interested in what he's interested in. i.e. if he's really into a sport or a video game or digging for bugs, you learn everything you can about that thing. Then, whenever you're together, throw yourself into that thing with him. Make that your focus. Do what he likes.

Often I find that when I put myself in my kids' world it brings us closer and I discover I have more emotion towards them.

Parenting his hard. Stay in the game. It will be better for both you and your son.