Im to nice and i think ive ruined my relationship with my boyfriend... please advice needed:(?

Okay well i use to be flirty before i fell for my boyfriend... but i mean just because im to nice.. i cant seem to say no (i mean of course cheating etc.. kissing yes id say no) but if they flirt with me i tend to ignore it and things and just cant seem to stick up for myself, but that is my personality and i hate it but now this guy has basically hurt my bf, my bf HATES him, they talk and all my bf does is fight with him and he tells the guy not to flirt with me but he doesn't listen, but tbh ive had enough of him fighting my battles and obviously it isnt working and i think my bf has given up... what should i do? im going to not talk to this guy anymore and things but is it to late? :( what could i do to make it better and to make him feel like i do care about his feelings, because i do, hes mor eimportant then my friend to me but the thing is that he is always busy and i dont want to say goodbye to a friend but i think i have to, to make my relationship work again?