should I leave him?

Should I leave my partner? im 18 and we have a 4month old baby.my boyfriend is 18.when I was 4months pregnant I had to go stay with my dad and my boyfriend went to tay with his (he didnt have to) he has a sister who was 14 at the time and her mate was also 14…just turned 14.my boyfriend was nearly 18.he ended up doing sexual things with the girl and then 2 days later he wrote to her saying he cant wait to see her again. I only saw the message and didnt know the full extent until recently.he swore on our unborn childs life he only spoke to her.however also when I was pregnant he used to leave me all the time to get cannabis (which he has now quit) and one night for the 1st time he pushed me over at 7months pregnant that I had to stay in hospital.while I was in hospital he masturbated to rape porn. he didnt care what he done. then just after I had baby about 3weeks oldhe strangled me and attacked me he has deeply regretted doing that though.now its boxing day and he has gone to his mums because we argued.he calls me discusting names and makes me feel uneasy to tell him how I feel.I dont trust him.I know I should leave him but I love him so much.it funny I used to read things like this and say LEAVE HIM!! but when its happening to me I now know how hard it is…please can the world give me advice!