This is a question that pops up periodically in my in-box and while I’m certainly not against the idea of warning women that their men have cheated on them, those warnings should only be given under certain conditions. Those conditions include, but are not limited to: being absolutely certain that the man in question did indeed cheat on the woman; being relatively certain the couple is exclusive; having the woman’s best interest as your main motivator. Unless all three of those conditions are met to the best of your knowledge and judgment, you really have no business crossing boundaries into someone else’s relationship.
I think it’s probably safe to assume your main motivator for telling Rick’s new girlfriend that she’s dating a “cheater” is not concern for her welfare. That you refer to both your bruised ego and your internal “little devil” in reference to reaching out to her sort of ruins that argument. Furthermore, you really don’t know that Rick is a cheater. All you have is Rick’s admission that there was a period where he slept with both of you. Well, do you know that they were exclusive during that period? Do you know that they had agreed not to sleep with anyone else? I don’t think you do.
I agree that it’s shady that Rick is continuing to text you sweet-nothings when he’s supposedly in a relationship. It’s equally fucked up that he’s repeatedly denied to you even being in a relationship. But that’s still not incriminating enough to contact this woman you’ve never met to tell her she’s dating a cheater … especially when your motivation for doing so would be revenge for the bruised ego you’re feeling now. Come on. You know that wouldn’t be cool. If you’re going to do anything, I’d recommend you delete the loser’s info from your phone and address book and be glad your relationship didn’t go further than it did. Be the bigger person here and MOA. He’s not worth feeling bad about your actions a few weeks from now when you’re no longer feeling burned.
*If you have a relationship/dating question I can help answer, send me your letters at firstname.lastname@example.org.