My boyfriend keeps on messaging other girls and lying to me. sorry its a little long?

I met my boyfriend when i was 14 and he was 17. We were young and i ended up getting pregnant. We have been together for four years, but through out our relationship he always messed up somehow. Two weeks into our relationship he cheated on me with his ex girlfriend and took her to prom and made out with her in the limo. He promised me he would never hurt me again. i took him back, but he started to act up again when i got pregnant. i moved in with him and i thought we were going to be happy, but instead i saw who he really was. i was never jealous until i saw all this.He would come home a 3 in the morning, i would always see him messaging other girls, he would go out and party with his friends and leave me at home. one time he called me the name of his ex girlfriend.I moved out of his parents house and went back home, but since then He has been messaging my sisters friends on facebook and there was a time where he wouldn't even come over. He would lie to me about going to work, and would delete his messages, hide his phone, he lied to be about smoking weed, and when i asked him for money when my daughter was sick he said he didn't have any, but the person that was with him went with him to the "store", but eventually told me he spent it all on weed. THere were also rumors that he had slept with this girl at my school and she said it was true. i remember seeing a message he sent to her about going to go smoke and hang out and her boyfriend told me they did.i just think about, if he is messing with girls i know,i wonder how many of them i didn't find out about. when i was pregnant it was so hard on me especially when you see comment on pictures where girls are bending over. in his words, "damn....can i?" it was hard on me and it is still hard even after four years. I am 18 years old now, and through out the months of nov dec and jan, he would hardly come over. he was always out and when i would go visit him at his job he would never be there. in December when it was his birthday he had his own party and forgot all about me. when we would see me with my girlfriend and my daughter he would say i was a hoe, just because he thought i was going to go do something. he constantly would put me down and there was a time he hit me. i told him to change for me, but in jan i found more pictures of girls that were drunk and were sent off to him. He did the same back. i dint know where he knows these girls from when he tells me he never goes out. there are lots of girls he knows and idk. he even hid girls number under different names so i wouldn't find it on his phone. i wrote him SO sooo many times asking him to change, messages that were pages long and all he said was, "Oh okay." and that was when i had it. i tried breaking up with him many times but he would always come back and hug me and kiss me and say sorry and it was back to the same things. after 2 months of seeing no change, i met this guy and slept with him. i know it was a mistake. i regret it and i didn't feel right about my self. i was really sorry and i kept beating myself for it. i still feel bad and i wish i could change what i did, i felt really bad and i couldn't live with the guilt so i told him because i love him and im not a bad person. i made a mistake like any human and i will never do that same thing again. i feel that so much pain he caused me made me lead up to this. there are 3otherstories on how he cheated. after i told him he says he wants to take it slow. he forgave me a few weeks later, but he constantly puts it in my face. i saw his phone and lately there has been more girls messaging him with revealing pictures and he writes to other girls. the friends that he had, that i thought i could trust, tried to set him up with other girls. it hurts really bad because he said and promised to start over with me. but i dont understand how that is going to happen when he is doing the same things. we got in the biggest arguement and i put his phone in the toilet because i got so angry from those messages and i threw a shoe at him and told him to go home,when he was supposed to sleep over. i feel that he is only using me for sex. he said he was really mad last night but when i told him i was sorry he hugged me and tried to have sex. i told him no and this morning he doesnt even talk to me. he says that i was messed up and that i am crazy, but i get jealous and i get sad that i may lose him. i know he is going to put the fact that i cheated on him in my face 24/7 and he even threatens me by telling me he is going to tell my mom so she can kick me out. i consider myself an attractive girl and sometimes i think i can do better. my boyfriend is not the best looking person out there but i love him for who he was inside back in the day in highschool. what should i do. i love him a lot and he is that father of my child, i just dont know what to do. should i say sorry,? should i work things out with