In need of some parenting advise...!

So I have a 1 year old and a 3 year old. And I’m 24 weeks pregnant. All boys. But I just can’t get through to my 3 year old... he’s perfect for everyone... except me.. His father ( my soon to be ex husband) taught him its ok to walk all over me ( hit me, scream at me, etc...) because his dad would also scream at me and talk down to me and hit me a lot.. I don’t know what to do anymore. I don’t know how to get him to stop... any advise???