So, they both know Terri is a liar. BOTH of them. Desiree had an instinct that Terri did something relative to Kyron disappearing - she "KNEW" Terri had something to do with what happened when she go the phone call. She knows Terri's lying because she's known Terri a loooong time. (Too long, it seems.)
Apparently, Kaine agrees - knows Terri's a liar. Yet Kaine let Terri raise his kids.
If I were Desiree, I'd have more than a little difficulty even standing next to Kaine.
Desiree had concerns about Terri all along but suppressed them for blended family's sake.
IMO, There's more skeletons in the closet ... lots more.