Have u ever loved someone very much and went off and hooked up w/ someone else to hurt them?

i just went thru a 2 yr relationship and we loved each other dearly. i kept complaining that she treats me like crap (bec she never did at first) and that if she wants respect she should show some herself. eventually some guy came into the picture and shes with him now. she chose to be with a player rather than a guy who loves her and her children. did she even love me at all? i dont understand how someone could treat someone so heartlessly at all.