I'm in a "healthy" relationship mostly because my GF has incredible relationship skills, the fact that I learn from them every time I see her, and our relationship is mutually understood to be "not forever". The latter reduces the problems that comes from high-stakes relationships, which ironically makes it healthier. Though it is debatable whether the ongoing success of a relationship that is by definition on spectrum below life-long but beyond LTR can be a datapoint for "healthy".
I have a close friend who has weathered quite a lot in his marriage, a lot of it similar to the dynamics that ruined mine. He perseveres nevertheless. Part of me sees "blue pill", part of me wonders whether his perseverance will pay off.