Why did my ex leave me for his babymother?

My ex recently broke up with my and went back to his ex he did this before a few months ago because she was refusing to let him see his child and she lied to the police saying he hit her and got him arrested and he told me he went back to her so she could drop the charges.
I only agreed to give him a second chance if he gave me his phone passcode and went to court to get partial custody of his child so he would not have another excuse for leaving our relationship and going back to her. After I forgave him he kept telling me he wanted to get married and have kids 3 months later we started trying for a baby. and I got pregnant he broke up with me and told me to get a abortion I found out he went back to his baby mother. After he told me to get a abortion he came to my house begging for a second chance and for me to keep the baby. I told his babymother about what he was doing and found out he was talking bad about me and my child to her.
After I contacted her he stopped contacting me he only contacts me to ask me to get rid of the baby. He also borrowed money from me before I found out he left me for his baby mother and he was living with me now he lives with his aunt. in the past when we lived together he would beg me for a second chance but now that he lives with his aunt he don't contact me and completely moved on with his ex.

Did he ever care about me?
Was he just using me and took it too far?
How can he tell me he wants to start a family with me and just change his mind in a blink of the eye and go back to his ex?
If he didn't want anything serious with me why didn't he just ask to be friends with benefits instead of pretending to care about me I told him in the beginning I would be fine with being friends with benefits
Why did my ex leave me for his babymother?
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