Why cant i get over my ex?

This story may not make alotta sense so jst take it srsly plz. Im 18 yrs old still very youn and i recently broke up with my gf of 7 months mainly becuz i was sorta falling out of love with her so i started talking to this girl who no lie is amazing like shes the whole package she beautiful And her personality is great ne guy would be happy right? Well i cnt necessarily say i am dnt get me wrong i rlly rlly ly like the girl but i still have my ex in my head all the time and wat kills me is since wev broken up shes acting like a totally diff person by goin to partys and drinking she even hookd up with a guy and now shes talkn to 2 guys idk if ne of them are serious talks but it still gets to me cuz wen we were together she bever did ne of those thing and i always wanted US to experience stuff like that...n i kno i nees to let her move on but idk it still kills me inside even though i have A good girl right now i jst think its cuz i dnt love like i did my ex and i feel like im jst doing this to show i dnt need her like honestly all i ever wanted was for her to tell me she doesnt want to lose me and for us to work on it And i wouldv stayd but it dudnt go down like that i kno deep down she loves me but she doesntt show it and thats wat i hate well idk way do u think?