I have recently found out that my girlfriend of 8 yrs whom i have two little girls with, has cheated on me for 2 of the 8 yrs we have been together. They went as far as calling themselves a couple. Before i had any solid proof, i had confronted the suspected person (her coworker) and he was swearing up and down that nothing happened and they were just friends, and blah blah blah and he would never talk to her again and apologized, well that wasn't the case he lied and kept talking, so i got sick of it finally and went snooping on the computer and found that she had a diary written to whom she referred to us as guy a and b, some of the diary entries literally made me sick. but regardless, after finding out the truth, i said i had gotten an anonymous call outing the two of them, and confronted both of them via facebook,(as they were both at work) the guy said he would delete her from everything and stop talking to her and my girlfriend denied it up and down, until she got home and i came forth with the info, So when she got home she went on to say that he was with her the entire time i was talking to him and even gave her a ride to the car after work and said he was just telling you what you wanted to hear. SO i made an agreement with him prior to learning this from my girlfriend, that if he admitted they were screwing around and agreed to some of the evidence i had presented, that i would not tell his girlfriend (who he also has two kids with) and possibly make him lose his kids cause he said and i quote "i would die without my kids they are the only reason i get up". Question, he lied to me and seriously pissed me off, now im a compassionate man and my whole agreement with him was based on my compassion for his kids not having to go through a potential breakup and lose living with both parents. I let him know he was an asshole for knowingly ****ing around with a girl with two kids and a fiancee. He put my kids at risk of feeling the results of a break up. should i tell his girlfriend that he is ****ing around? does she deserve to know? and how would i express that to her given that i dont know her? im really torn with this one, In my head i know its the right thing to do, she doesnt deserve to live one more day without making up her own mind on whether or not to be with this asshole. please help!