How to handle a girl flirting with your crush?

my ex and i broke up a year ago and i have feelings for him again. my friend told him that i liked him then he started ignoring me. my friend kept on asking him to come and tlk to me and if he liked me back but he would always say its for me to kno and for u to not kno. so at my party i really didnt wnt this girl to come but she did and she started flirting with him and he flirted back and followed her like a puppy. my other friend tht likes me kept on putting his arm around me and my ex would always stare at me whenever his arm was around me. then we played truth or dare and he was dared to kiss me. he got up and was trying to move my head to kiss me on the lips but i moved away cuz i didnt wnt him to kiss me infront of everyone. so he kissed my cheek and then after started flirting with the other girl. after the party i turned awayy from him and he grabbed me for a hug. i kno this is long but i need some advice. either to keep on liking him or having the other girl have himHow to handle a girl flirting with your crush?
oh that has got to hurt and i dont blame you for being kinda jelous at all. I would totally just talk to her about it nicely maybe joke around and say: hey ya know __insert guys name___ is totally mine lol. i have done it before and she got the message and backed off. good luck and get him