Trying to find a song!

I'm trying to find this song that I heard on the radio a couple of weeks ago. I don't know if it's an old song or a recent one. This is pretty much what I know about the song:

It's sung by a woman.

It's kind of maybe R&Bish?

The song is about a lady (the singer) who receives a letter in the mail addressed to her boyfriend/husband, forwarded from his old apartment (or house?). She opens it and discovers that it's from an ex with whom her husband had a secret love child. She then goes on to sing about how terrible this all is. I have a tiny snippet from what I remember of the lyrics too.

"What about our future? You messed up our (or the) plans because you couldn't keep it in your pants."

I tried googling that (and a few variations) but came up with nothing. If anyone recognizes this song, I'd be greatly appreciative. : )

Thanks.

ohoh, i remembered another tiny tiny detail. At one point she says, "when were you gonna tell me?"