Oh dear, OP, i read through this entire post and just wanted to tell you, as lots of others have done, that having low self esteem isn't something that just happens to us, its a lot to do with how we treat ourselves, and how we let ourselves be treated.
It's clear from this thread (think about how you would feel if a friend told you this long, sad story, or even your daughter or granddaughter...) that you are allowing yourself to be treated as second best by this person, who cares a lot less for your feelings than for the feelings of other people in his life.
What can you do, to feel better about yourself and boost your self esteem? Put yourself and your DC first, tell him thanks, it's been great but please don't bother me til you have got yourself sorted.
Then focus on you, and your DC, and build a great life without him.
It won't be easy, but it will be rewarding. It is entirely up to you, which person you will be in ten years, the one who hung on, asking perfect strangers why he keeps making excuses about things important to you or ... the one who has built a great life? All the best, xx