How do you deal with a disappointing parent?

This isn't new, and I have never found a solution. Since I have another LO due this spring, it really feels like everything is being brought up surrounding the situation. There has never been any progress with this person- so it isn't a simple "tell her how you feel."

Basically she offered to come help when baby is due, but only several weeks before or several after the due date. Obviously the help I would need would be when the baby is due so that someone could watch LO1. It is also her birthday.

The heart of the matter is that she has never been there for me. She remarried and constantly tried to have new kids and then did it again and kind of left the original kids in the dust. (I was an original.) For example, she built a new house when I was still a new teen and did not build a room for me and I had to live down the street alone. There was a room... but she gave it to her new baby (who didn't need it, and money was no object.) With this situation, I assume she has some dumb thing she would rather do concerning her new kid (an upper teen). Like a track meet dumb. I use that word because I would love for the birthday and birth of her only grandkids to take precedent. She skipped all of my sporting events and left us home alone while she toured the country with men. So now all of a sudden she is the best mom but not to me?

That is just one example! So now with her new kid she gives 1000000%. I have all of these things built up and I need to address them with her but she doesn't care. She just tries to manipulate me out of how I feel and denies things if I bring them up. Typing this, I think I know the answer.

However, I am not sure I want to break it off. It is my only mother, however a shitty one.

I don't want to come off entitled in some way. The lady completely ignored me from a young age when she remarried onward and there was lots of domestic violence, drugs, abuse, and a suicide (stepfather) in there. When she left my dad it was over night, when my stepdad passed she was remarried within a year. I wouldn't be surprised if she has some inability to love or attach, that's how it seems. When she left my dad it was as if a switch flipped and she kind of threw our family away- there weren't major problems or anything. Dad and I were pretty devastated and it sent him into a downward spiral and he eventually took his life last year.

Thanks for caring if you do. I keep my horrible life hidden for the most part IRL except with a few close people. It is hard for me to open up about it (not only my childhood, but my present whomp whomp).

Do you have a crappy parent? How do you deal?