If you are in love with someone it's probably not wise to start having any sex, paid or otherwise, with anyone else. Tends to spoil it. Also you will see people every day of your life you find attractive, there is a reason you chose your partner though. Unless you were just desperate, and jumped on the first wife material girlfriend you saw. So, unless you get off on risk, which will only get worse, maybe don't do it. Or, let the lady find someone else who will be at least initially monagamous and and you go off have as much fun as you can get
If you are in relationship its also unwise to practice any kind of unprotected sex, unless you feel able for the inevitable risk. As to how selfish someone maybe to do so, we all have our sins, its if you can live with yours or not that counts.
I'm screened often thank you. I hope you are too