From the Big Baby thread:
As for healthy relationships have we ever seen any character on the show in a healthy relationship? I mean that seriously. I can't think of anyone, doctor or patient.
Occam's Razor (parents and son; son and fiance)
Maternity - the Hartigs (Max's parent) and Chen-Lupino
Detox - Keith (POTW) and his father
Heavy - Jessica (POTW) and her mother
Daddy's Boy - Carnell (POTW) and his father. (Yes, there were a couple of lies, but not to the point of the relationship being unhealthy)
Distractions - parents
All In - Ian and his parents
Fools for Love - it was a healthy relationship until they found out that they were siblings
Merry Little Christmas - dwarf mom and daughter
Family - the entire POTW family
"Happy families are all alike; every unhappy family is unhappy in its own way." Tolstoy
With only a few exceptions (e.g. Family) the functional relationships are not front and center in episodes because the drama mostly comes from the unhealthy aspects. But there are examples of ehalthy relationships on the show.