I just found out I was the “other woman.” I thought my boyfriend was single but apparently, he’s been married for four years. Do I tell her?
I’m sure I’ll lose the popular vote on this answer, but girlfriend to girlfriend, my advice to you is nope, you don’t tell her.
“If it were me, I’d want to know” is something we hear a lot in these circumstances, and while that might be true for the wife, it also might not—and you have no way of knowing what this woman wants.
You don’t know her. You also may not know what kind of marriage her and her husband have, or what she is or isn’t aware of (or is or isn’t okay with). You are not the wedge in their marriage. This one isn’t yours.
I’m sorry you had to find out about his marriage the hard way. That must have been very painful. Please do your best to dust yourself off by having a friend or a coach hear you out on how he hurt you so you can clear the pain out of your heart. I want you to be able to look at the next one with fresh eyes instead of as just another soon-to-be cheater.