Pay bitch

A person whose existence is for the purpose of paying for other people. Typically refers to a woman and/or the head of a large household, but this applies to anyone who gets suckered into paying for others.

My girlfriend makes more money than me so I always dupe her into paying for everything. She is my pay bitch.

pays the bitch

(idiomatic) To provide enough money to cover basic necessities.
similar in usage to "puts food on the table"

"Hey, how is that job at McDonald's?"
You know, it pays the bitch."