Texting a fuckbuddies girlfriend that I had no idea about

Alexis

So I had been fucking this guy for a while and I just recently found out that he had a girlfriend. I want to tell her because you know girls have to stick together. But I don’t want him to find out it was me because he has something on me that would ruin my reputation. So I made a Instagram account that no one could know it was me, but Idk what I should say that makes it were it doesn’t sound that me. Help me pls

*Update*

I confronted him about it he’s just denying that he has a girlfriend. So I left a empty ripped condom wrapper in his truck on the passenger side. After that I just broke things off with him. Thanks y’all for the suggestions!!