What to do when you like ur use to be friends ex!!?

k so heres the story making it short and simple i had a friend she was like cool and we were juss tight then when her ex moved littery 1 house over it made are frinship akward cuz i didnt know he move there until she intrudouced me to him and then we hung out but everytime when i wnated to hang with her she always wanted to hang with him and i didnt have a problem wit it but still it juss gets me then cuz i really didnt kno him as were nieghboors we decided to hang for 1 day and get to know eachother he keep flirting i was feeling weird cuz u know its her ex i was gonna tell her but it was to late she tottaly jump to conculsions and said its my fught didnt belive my side of course and there was are frieindship and then i still talk to him cuz hes like right by me and we are flirty but is it wrong or not somtimes u cant hide what u feel i mena am like stuck cuz i got feelings for him ?