It's such a taboo area, and that stigma means it's hard to work out what's going on and how to deal with it.
This is why I suggested a counsellor, who would help you dig into it, and who has expertise so it's not the blind leading the blind!
I have a mother who clearly adores my sister and had me because my sister needed a sibling, and that's all I ever was. Luckily my sister and father didn't follow in her coldness, although they kept any loving bonds very quiet to avoid the consequences. My mother was rabidly jealous of me getting any love or affection and really couldn't see any issue in putting all sorts of disgusting oedipal vileness on my father and me. Destructive, disgusting, nasty woman. She also expected to have everyone dancing around her when she was eaten up by jealousy when DS was born. She did her best to push me out of the way, and be my baby's 'mummy' instead. Not a nice person.
Anyway, the point is, my mothers lack of love or bond with me was very damaging. But this is different from what you are describing. It was what she did because that lack of bond that was so awful and cruel. When I speak / write about the awfulness of my childhood, I am not talking about you!
You aren't allowing a problem with bonding turn you into a cruel and abusive woman. You aren't letting the less strong bond act like an open doorway, a gap that enables you to venting your spleen and letting all the warped sickness out.
And I think it's really important to remember, and believe in your heart, that you aren't a bad person because of the difficulty bonding with your son.
It's what you do with that problem which defines what kind of person you are, and what legacy you leave in your son.
Working on strengthening that bond, and also working on behaving as if you already have that bond are two different ways to address this situation. Doing both in tandem sounds like the best way forwards.
But, to be able to let yourself acknowledge and explore what's going on, I think it's important to stop judging yourself /let others knee jerk judgements get in the way.