In relationships, there are many cases like that , just like yours. Some love is not understanding each and other and causes many hard feelings for both of you and makes you partner to betrayed you and she might find some other who can understand her better .That is usual in relationships, think about it the cause of your separation .Being betrayed may makes you angry and uncomfortable but just think once , it is more better then she is with you and betraying you at the same time , it is more hurtful . Feel her alone and let the new love finds you.