i love my boyfriend but i don’t know if i should break up with him

okay so my boyfriend and i have been dating three months but been talking for over a year. anyways he is a natural flirt but he doesn’t mean to be and he has a lot of girl - friends. meaning friends with girls and he flirts with them all the time. and i know hes loosing feelings and i can tell but i absolutely fucking hate myself and i’m just ugly and annoying and fat and just a piece of shit and i don’t know why he’s with me but whenever he talks to another girl i get so cut because i’m scared we will leave me for them. so i cause an argument about it and it just makes it worse. so i don’t know what to do. do i break up with him bc i love him too much or do i stay and try to sort shit out. :((( cox