SPOILERSAnd she's supposed to be important, right? This story has eight episodes and tries to tell the end of a marriage.
Surprise: the fucked up cop fuck young chicks (fucking gorgeous chicks who just want to fuck him, but let's not write about him having a relationship with someone; they're young and want to fuck hum: it should be enough.)
Surprise: his wife fucks Cohle (who's just there since episode one waiting to fuck Cohle, they weren't subtle about that.)
It seems trivial in the way you describe it, I see it in a bit different way. Some quotes from the show:
Rust: I don't think that man can love.
Marty: Yeah, I'll tell you guys and believe me, past a certain age, a man without a family can be a bad thing.
In a way it is exact opposite of what they want. Relation between Rust and Marty works as a story, because they are in stark contrast. There is a bit hypocrisy in what they say over and over again: Marty talking about importance of rules and breaking almost all of them and Rust talking about consciousness being an error in human evolution, yet behaving very strict.
Why their friendship works? I think one wants to be the other. It is pretty clear after sex scene that Rust was looking for something more than sex: being close to somebody else, having a family, mowing lawn. Marty on the other hand doesn't want to grow up and settle with family: he wants to be a Cowboy.
If you look at marriage dissolve as just divorce, it is trivial. "True Detective" as of episode 6, for me is about lives of two detectives, their personalities, believes and differences between them. In a way both Rust and Marty are cowards, because they cannot honestly acknowledge what they want from live.