Three way

So my husband and I where watching tv and a girl was married and slept with a girl behind her husbands back and I said she cheated he said if I slept with a girl he was fine with it. That he wouldn’t sleep with anyone besides me but that it was okay for me to fuck girls? So I’m confused as to how that would work I wasn’t even thinking about it till he mentioned it any of you have any advice or stories?

Ps. I have been interested in a 3sum before but want more information ya know?