LF: Guy forced by bi/les to have his girlfriend sleep with her

[naughtierxxx]

Guy is forced / reluctant to let the lesbian/bi have her way with his gf... maybe a bit like the r/SheStoleMyGirl sub, but with his knowledge of whats going on and without his gf's consent (at least initially), so gf can be forced / trapped too!
What is this fetish/situation called? Stories / tags appreciated!