>tfw is typically "that feel when"

So i can assume it means "that feel when girlfriend". No idea why having a girlfriend would make you work nights? This would make more sense in the context of

"that feel when no girlfriend"

I interpreted it from the perspective of the girlfriend. That is, her feelings on the the significant other being gone essentially the entire day.

my uninformed guess is the face when girlfriend

using my license to conjecture, I'd say that OP has a girlfriend and thus has a lot of expenses that a single man would not have