And the real sad part is.... 'Once a month' is a maintenance-fuck. Like, she really doesn't want to do it, but for whatever reason, she continues to do so.
I don't want to feel left out, so I'll make my list like everyone else....
1. Shes afraid to be alone
2. Shes fucking around on the side, but she knows the side project would never want her as a main course (see #1)
3. You make more money than her... but not that much more... otherwise you would be getting it more than once a month.
4. Shes a closet lesbian.
5. You have bad hygiene, small dick, big dick, fat dick, skinny dick, (red dick, blue dick?

) , can't fuck, sex is too routine etc etc... this goes under the header of "Can't get no satisfaction."
6. She wants to be with someone else, she just doesn't know who that someone is yet. (see #1)
7. Some kind of drug shes on could have killed her sex drive.
8. You made it all up.