i was the second girl didn't knew of the first?

I've known him from work i was never interested in him cause i didn't wanto risk falling in love again..and i wasn't attracted to him but i risk it , and we've gone out a few times, yes we were sexually active and he was such an adventrous guy i became attached to his ways he treated me so nice, come along way just to pick me up see me veryy kind indeed we laughed after sex during sex in the car every where but.. saturday last week me and him went to a beach party at first he didn't want to go because an ex girl of him supposely was going to be there.. at that time i already suspected him and i told him be honest with me cause if you are screwing another girl tell me cause i don't mind as long you tell so i can do also what i want you know what i mean after i convinced him to get out (mayor fight) we sat had some drinks etc... then the ex girl came with a friend of mine in class imediatly when he saw her he went to his car.. after that i saw the girl heading his way after a few minutes the girl in my class told me her friend (the ex was also his girlfriend) i was shocked because i didn't knew he had a girl if i knew i would never done such a thing... no it's been 4 days i think and he only called me 2 times today and the night i found out.. i mis him extremely but i don't wanna go backk to him cause i feel bad for the other girl which he seeing fo 3 years and me only a few months.. soo if you were in my situation would you call him back cause i didn't talk to him nor spken to him for these 4 days.. i'm trying to get over him.so i won't take him back .if i pick up. i just wanted to know what would you do?