My bf cheated on me and im pregnant with twins and i have a hard time ending it..?

helpppppp! so my please dont judge me i need really serious answers...im 17 and pregnant with twins and my boyfriend who really does love me cheated on me after we got in a little fight... well this is the third time hes cheated but first time hes actually had with the girl.. not only did they hae sec but he brought her to our friends house and cuddled in front of all my friends... when i found out i went there... i saw himand her adn everyone else chilling and i bc im preg i didnt do what i wanted to do to that little b****** anyways so then i talked to him and he still wanted me bc im his baby he really loves me ... but now i find out hes been doing some bad stuff like drining and some drugs and like idk i dont want that kind of guy plus i can never stop thinking about how he was with her... so i tried breaking up with him but i see him everywhere.. our friends are all the same and i have trouble keeping away from him.. i get soooo jealous when i think hes with a girl.. its like hes my man and i have his babies in me but i know hes not good for me but how do i keep myself from going back to him its like i dont wanna be with him but i dont want another girl to have him... maybe its my pregnant hormones talking and im not a selfish person i dont mean to sound possesive but he is my baby daddy and i know him like no one else does.. hes my bestfriend.. help me my life is crashing down.. i tried to chill with my girlfriends and stuff and act like im busy and doing ME but it dont work... ive changed my number and evverything i feel stuckk. how can i stop loving him..