Please help figure it out why she did this to me?

[Paul]

Me and my ex fiancè lived togheter for about 3 years , we broke up because the last months we had lot of drama and we didn't talk for quite some time , after a month she got back with her ex Bf which me and him fight a few times because he was stalking her , when I knew that she was back with him I started dating a ex friend of her , my ex got jealous of this and start insulting me for a while and I just ignored her , time passed and I meet her 3 months ago and we talked about all the drama we was throu and decide to stop acting childish and she left her ex and I left her friend ,even though we didn't back togheter , we did this for respecting the times togheter , me and her stayed friends but we had sex almost everyday , she said that after all she feels good because I was her ex and she's single. one day she told me about this dude she text with on twitter , she gave an apology because she didn't knew this guy knew me , she said Im embaressed sorry for this , I appreciate it that she told that and I told her to don't worry about it , then she told me that she will never hang out with him out of respect of me. during this months of "friendship" I've always been there for her , for whatever she needed or just for hang out and sees eachothers , I felt good because when I was with her sometimes I was jerk and seeing her that still wanted to see me it felt good to have someone who cares about you after all the B.U.L.L.S.H.I.T we been throu. I've been in Holidays with my family and when I got home I saw her putting pics with this guy and now they have a relationship , she text me a few times without mention it , but I didn't replyed because I feel hurt, Why she did this to me? You think she played me all this time? Im very disappointed because I've been with her for everyday during this 3 years , I knew her family and she knows mine , I lived with her here in the States and in Holland , she even had my moms home's key! I know that she was not my girlfriend anymore , but then why made me this promises and why she did even come back first? Im really losing my mind for her now.... After all what happened to me I don't believe in love anymore.