Helpp! my ex is ruinin my life again!):?

Uqhh im so mad i allready got over my ex n i dont want to get feeling fo him again.One of my problems is that i mostly always have to hang out wit him cuz ma bff is his sister bff n then i always walk wit her n he got to come wit us,And last time we had this fun thing at skool n she was their so was her brother n i didnt wanna be wit them cuz it was akward but my ex was actin strange too he wasnt checkin out any girls or flirtin wit any n he always does wether his single or not that was jux a shock to me but he kept bothering(Mo info in my"why he actin strange"Q) me.And then everytime i have to see him at skool.N ppl always be bringin me news about him.Like this day one of my guy friend that is his friend too asked him if he ever went out wit me n he said no.N i dont get it why he has to hid it was he ashame of me cuz really im not Even ugly n most of his friend always wanted to go out wit me.i gave him all my love for this **** n wat i hate the most is i gave up our frienshipp.Why did he actin this way now!