A basic summary of how "The Losers Club" polycule happens in my stuff:
Angel and Cherri are basically friends with benefits for a while. Mostly just hanging out, but occasionally hooking up casually. Then Angel gets into a relationship with Husk, but the relationship is an open one, since he does still like having occasional one night stands with other men, and his thing with Cherri.
Husk, being actually good at reading people, eventually gets Cherri and Angel to get that they want to be/basically already are, more than just the friends with benefits, so he just tells Angel to bring Cherri into the relationship officially. Husk and Cherri technically start out as just "friends" who are dating the same person, but do eventually end up considering themselves dating.
Pentious literally invites himself into the polycule by accident. He gathers up the nerve to ask Cherri out on a date, either not fully realizing she's with Angel and Husk, or (correctly) assuming the relationship is an open one. And when she playfully asks him why they should date, he has a panic moment and announces he's dating everyone present - which just so happened to just be the current "Losers Club" in the room. And the rest is history.