co-parenting after a LS-related split, how do you not pass the chaos to the kids

we've got two kids 9 and 12. their dad and i split a yr ago cuz he developed feelings for someone in our LS group and refused to give her up. fine, whatever, we're past that. what i'm struggling with is co-parenting when half of his current social life is people i used to drink wine with. the kids occasionally mention "dad's friend sarah" and i have to keep my face completely neutral while inside i'm screaming. how do you do this without poisoning your kids against him? they don't know anything about the lifestyle obviously and i never want them to know but they will absolutely pick up on tension. any divorced LS parents got wisdom on this... drowning here