Portable Sidepiece

A sidepiece who is ok with and even happy to be your sidepiece even when you break up with your main piece. A portable sidepiece has no aspirations to be your primary relationship and will remain with you through multiple primary relationships.

Person A: I broke up with my boyfriend.

Person B: So your side piece is gonna be your main now?
Person A: No, he is a portable sidepiece, I can take him with me to the next relationship.