My boyfriend and I have been dating (and living together) for almost a year. Recently, he left his email up and I saw a lot of emails from his ex-girlfriend. I clicked open one of them (from her) and read the short paragraph that amounted to, essentially, cyber sex (her imagining which position he'd use on her).
I told him and he immediately apologized (of course) and sent her a text message saying that he had to stop, was very much in love with me, and didn't want to continue talking to her. (She responded by asking if I knew, then threatening to tell me if I didn't already.) He deleted all communications, and blocked her on Facebook.
He's been truly remorseful and said that he had been feeling guilty about the exchange--was almost glad to be caught. They had been flirting/sex-emailing for about a month. She sent him an email saying that she thought about him when she has sex with other men or masturbates. She lives in a different state and has mentioned coming to visit, but my boyfriend says he really has no interest in being with her physically--only the fantasy.
He has a history of cheating (I started dating him before he broke up with his last girlfriend), but mostly it's about not being happy in his relationship. He says that he's made a huge mistake in talking to his ex and that it's made him realize just how lucky he is to have me.
I think that this is forgivable and that I understand him wanting to live out a fantasy (though neither of us think that involving another person, especially an ex-, in a fantasy is acceptable). I just want some advice on whether this is really serious.