My ex-MIL remained not only friendly with, but remained business partners with, her ex-husband for YEARS. She and her BF of over 20 years go to events hosted by her ex's family, and her ex's family is welcome at her events as well.
It's not unheard of among mono folks.
Mono. Divorced, two kids (DanceGirl, 13; and PokéGirl, 11), two cats, one house, many projects.
My partner. Poly. In relationships with me, Xena, and Noa.
Poly. In relationships with Chops and Noa, and dating others.
Married, Poly. In relationships with Chops and Xena (individually).
Blog thread: A Mono's Journey Into Poly-Land (or, "Aw hell, there's no road map?!")
Slightly more polished blog with a mono/poly focus: From Baltic to Boardwalk