How do you say your done to someone abusive?

i have a 5mth old baby with my ex boyfriend? i haven't been perfect in our relationship, when i say perfect i mean just giving attitude, and telling him that i would sleep with others i know that was wrong, but i will tell you why, i kick him out only for a day and now he cant get over it, so he found his own place, the question i would like to ask is that i recently found out that he cheated on me with his babymother when i was pregnant, left me for three mths to try to work it out with her, but it didn't work so i guess he came back to me, i just found this out last week, and on top of that he confessed to having with some other girl, we werent together but what bothers me is that when we got back together he continued to talk to her, i found texts where she was going to his house, i confronted him he said she came to get some papers,lol and then i also found out that he has been having with her for two mths while we were together, and last mth she thought she was pregnant, mend you he has not confessed to this, and on top of that he hits me, last week he gave me a black eye, and bust a vessel in my eye, and strangled me, so i am pretty much done, but how do i break it to him, i have tried but he doesn't seem to get it, how do i let him know its over and that i only want him to come see his son thats all, everytime i try to tell him this over the phone so that he doesn't hit me he just hangs up before i even get to tell him anything.> so how do i do this please help