I seriously want to know what his and his wife's agreement is. She know's how he acts around these girls, she's ok with this? It's just weird.
Well, mommafitz and Fitz weren't blessed with children of their own. Thus, all of these great gals and guys he meets in Aggieville at 2 am are like their kids. Eventually, the kids move on like seeds scattered to the wind.
Also, I bet Fitz tells her he has to work late, she doesn't want a drunk/stinking Fitz coming home and climbing on top of her trying to get laid every night so she deals with his creeping.
The fact that they were both barren is just a bonus to future generations.