A few years back I was looking to start up a FWB relationship. I'm married, but have a drastically mismatched sex drive with my wife. While I would be good having sex 2 or 3 times a day, she's more like once every 2 or 3 weeks. Needless to say I end up wanting it a lot more than I get it. I won't claim that justifies infidelity, but that's where my head was at the time.
I put out the following ad on Craigslist: