Why does my boy friend/kids dad hit me even when i am prago with his childand we have a 5 month old?

we have a 5 month old lil girl and i am 14 weeks pregnant and when i was not pregnant he has really hurt me bye kicking me and pouching me and he has even bet me be for and he all ways drags me around by my hair,, it don't happen every night just about one time a month..he say i piss him off and i don't shut up and i ***** at him.. i don't know what to do i have know family and know were to go i just wont him to stop and have a family to gather,,, he is in anger mng classes for about 6 weeks and he was good till to night..well he had smacked me in the face ones sins his classes.. i wont to help him but i don't thank i can i don't wont this for my kids... but i wont my kids to have a family...