I miss my ex but i have a new boyfriend?

i dated this boy for a year and we were really good at first but we both didn't know if it would last. we were eachothers "first's" for everything and we both were never in any serious relationships. we started dating in april and then by june we were in love. the only thing was i faught with him over every little thing. be broke up for like a week once because i was so mean. he didn't care though he loved everything about me. after about a year i broke up with him because i knew it wasn't right for me to be yelling at him all the time and being mean. we didnt really talk for a couple weeks but then we started hanging out again all the time and acted like we were dating eachother but we really werent. then my bestfriend and i fell for eachother and we started dating. its only been 2 months but i really miss my ex. but it's only when im alone and i really think about it. when im with my new boyfriend i totally forget about my ex and everythings fine. me and my ex still talk all the time and he begs me to break up with my boyfriend all the time, but i dont know what to do. if me and my boyfriend breakup he wont be my bestfriend anymore. things probably wont be the same between us. but i miss my ex.