Rob and Kevin play cartoon versions of Vulcan versions of themselves with the help of their exes in "Four-and-a-Half Vulcans" (SNW). They then revisit past episodes where post-relationship relationships figured prominently in the stories of Starfleet officers, including "Haven" (TNG) and "Rejoined" (DS9).
SNW 3×08 Four-and-a-Half Vulcans
SNW 3×07 What is Starfleet?
SNW 3×05 The Sehlat Who Ate Its Tail
Exes
The Wonderful Masculinity of Commander Riker (Rowan J Coleman)
TNG 1×11 Haven
TNG 1×01/02 Encounter at Farpoint
TOS 2×05 Amok Time
DS9 4×05 Rejoined
DS9 6×26 Tears of the Prophets