Fuckship
The word used to describe the relationship between you and your fuckbuddy.

An association between two or more people that is limited to regular sexual encounters.
"Oh, they are just fucking- it's a total fuckship they're in"

"We don't talk, we dont hang out, we just screw. It's a fuckship"

They've been seeing each other for sex for the past ten years. It's a fuckship thats lasted the ages"