Shit happens, just make sure to learn from your mistakes. It sounds like you might want to begin emotionally distancing yourself from her as well, as things sound like they are heading towards the end. My ex used the excuse of "Ever since Robby died(my best friend that died in a car accident last September) youve been different" NO FUCKING SHIT... YA THINK????? Then for the last few months while she was flirting with somebody else she began to distance herself from me more and more. Its for the better though. If she cheated after almost 4 years, she will definitely cheat later on down the line. At least thats how I see it.

You shouldnt have taken her back after the first time she cheated. People that cheat and dont at least have the excuse of being absolutely wasted have cheating in their blood and most likely will never stop.

Not saying everybodys the same but... well ya know.