Most Helpful Girl
Sadly, yes. Twice.
Both times I'm not sure if he (two different guys but I'll just say he) slept with the other girl or even did anything with her but he was talking to or seeing her (one on one) before we ended things.
First guy after being with me for 9 months went out on a date on Valentine's Day with some girl he met online. Found the account and e-mails on MY computer because he was basically living with me. He said he was having dinner with is mom because she was sad (her mom - his grandma died around that time the year before). I was gutted. I'm not even sure why I never got up the courage to tell him I knew about this but it ended pretty abruptly after.
Second guy... together for over 3 years, living together. He meets some girl at work...11 years younger than him! He's acting squirrely so I check his phone I find texts some to her him saying he's spending all day in bed with me watching sports and her saying she was jealous... I couldn't really tell if that was just her being jealous he had someone or more than that. Then his cousin texted him something about did he want something to happen with her. Since I was snooping which was wrong (I know it;s wrong) I didn't say anything. But I tried to figure out what was up... about a month later he said he just wasn't good enough for me. Everyone expected us to get engaged and he said he just didn't know when if he could do that. He started dating the girl form work almost immediately... they were on and off for over a year and every time they were off he ran back to me. I'm actually pretty sure more than once he just said hey were broken up but that wasn't how she saw it so technically he cheated on her with me too. He married her last fall. I say... she can have him I don't want a cheater.
Honestly though, it shakes you to the core and makes it really hard to trust anyone in the future. it's not just painful at the time. It causes scars... emotional scars and it affects you for years if not forever.