Not to write an essay about it on this thread, but there are known trigger points in abuse becoming a factor.
These commonly include: Buying a home and moving in together, pregnancy, marriage, the birth of a baby. They are all scenarios in which an investment has been made and therein, an undeniable degree of codependency. In the case of a baby, that investment is irreversible.
In short, the abuser knows the target is not about to up and leave so they feel much more at ease in indulging their abusive traits.
This is not my opinion btw - you can readily find this information via credible domestic abuse resources online.
Add to that unpredictable, life changing personal circumstances that occur such as illness, bereavement, trauma, substance abuse and so on, it is not difficult to assume that he wasn’t always a blatant nasty bastard and that the OP acted in good faith when she had children with him...just like the smart arse with all the answers did when she fell in love with her husband.
“At what point in the relationship did he start behaving like this?”, is quite different to, “And you had children with this man, why?”.
The inference that the OP has found herself embroiled with an abuser through stupidity, is actually pretty galling.