classic lovebombing cycle. He can't change that fast from abusive person into not abusing you. Abusive people can change, but it takes an amazing amount of internal work and time. He needs to go to therapy to figure out why he acts like this and work on not enacting his trauma/feelings onto other people. In the time he's doing that work, he's not a safe person for you to be around and you need to get away from him for your own safety. I'll also remind you that it's not like you'll just lose things when you leave, and keep things if you stay. If you leave, you gain a lot (not living with an abusive person, for one), and if you stay, you lose a lot (living with someone who mistreats you).
I will also say this as someone who grew up with an abusive father: my parents divorce was traumatic, but as soon as my father left the house, I began to get better. I didn't realise because i was so young, but my father being in the house and witnessing him abuse my mother really messed me up. It was terrible and has left me with a lot of trauma still, and has left me with really fucked up understandings of what love looks like. The divorce was hard and painful, but it wasn't half as painful as living with an abusive man as a child. He never 'technically' abused me or my sister, but he didn't have to - watching him being cruel to our mother was traumatic enough. If you don't want to leave for you, leave for your kid. By leaving, you teach your child that they shouldn't accept mistreatment in abusive relationships: in staying, you model that it's ok for them to hurt their future partner, or for their future partner to hurt them.
I'm so sorry that you're in this situation, and I am really and truly sending you and your child support and good luck.