I feel for you. It took me a long time to come to that understanding both with my father/family of origin and with my now-ex husband. They are who they are. They kept telling me I was the problem but no matter how I twisted it, I couldn't see any thing I could have done to make things better. They are who they are, in my father's case, an alcoholic, in my family's case the dysfunctional result of living with an alcoholic and in the ex-husband's case, the adult child of an alcoholic who refused to look at himself and admit and fix his habits of lying and all that went with that.
I kept thinking I was dealing with 'normal' people who sincerely wanted the best and were open and honest, blah blah blah. That's not what we're dealing with. Eventually, we figure it out.