Toxic relationship with baby daddy?

So. Me and my fiance have been together for 2 years. He has a 4 year old daughter from a previous relationship that he has 50/50 custody of with a week on week off arrangement. I moved in with him about a week after we started dating due to him breaking his hand (by punching a tree) and being laid off work. I moved in to help cover the bills and help him take care of his daughter. 2 years later we are still together, and now engaged and I am 23 weeks pregnant with our son. He is a really good dad, I watch him with his daughter and he is great with her and loves her very much. However, he is not so good with our relationship. He constantly holds the fact that he pays our rent over my head even though I do all of the house work, pay for all of the groceries plus the internet and I take care of his daughter, from waking up extra early on weekdays to get her ready for preK, packing her lunches, doing her hair, giving her baths, taking her shopping, taking her to her dance classes on our weeks etc. He also likes to tell me im stupid and say I'm "just a stupid woman who doesn't know anything" when we have a difference of opinion. I am a full time college student, I work part time and am basically a full time step mom to his daughter every other week. I am far from stupid and he really hurts me when he says those things. (And yes, I would like to add that my pregnancy was not planned and I had been considering termination but couldn't follow through with it so here I am). He has even gone so far as to drag me accross our house yelling at me and leaving bruises on my body simply because I refused to sleep on the couch after we had a fight, I was also about 10 weeks pregnant when he did this, (I will add the pictures I took of the bruises he left on my body from this). Our relationship has never been prefect, and I can also say I dont really know what a good relationship is supposed to be like, im 22 (hes 32) this is the first man i ever kissed, ever had sex with and ever dated. Now we are engaged and having a baby. I feel like this is a very toxic relationship but I still have a hard time walking away from it. I feel so stupid and I just dont know what to do. Things have been pretty decent lately but I still feel like I'm walking on egg shells around him sometimes and I know that isn't healthy. But I also don't want to leave and then have to share custody of my son with him.