One is my primary partner (we’re non-monogamous), and one is a regular FWB. The third was a one-time thing with an old friend.
Basically I had a chance to meet with my old friend and she had always wanted to have sex, so we did. My FWB gets really turned on when I mess around with other people, so when I told her, she wanted some too. And later that night I think my primary partner just wanted to assert dominance over the other girls, so we did it again…
At any rate, it was exciting, fulfilling, and exhausting.