King of Pentacles as the Relationship

Brilliance

In my opinion the King of Pentacles could represent a relationship that ends up being a marriage. It definitely symbolizes a responsible, both financially and emotionally stable relationship. Perfect for havings kids as well. King of Pentacles isn't as emotional as the King of Cups would be but I wouldn't say that he is an unemotional King. That would be the King of Swords.
 

Barleywine

This seems like an instance where a court card would represent an impersonal energy or force at work in the situation rather than a specific individual or personal characteristic. The King of Pentacles suggests "slow growth;" Aleister Crowley called his version "the smouldering fire of the process of growth." If enough patience and forbearance are applied, stability would be the expected outcome in the (possibly very) long run. The question is whether either party is willing to put in the effort or to wait that long for results. If not, the relationship could take on the qualities of Crowley's other observations: "dull, heavy, laborious."
 

obeygravity

I think this may be a card where my experience greatly differs from most people's.

The KoP for a relationship would make me slightly anxious. In the past this has shown as a person or a situation that's exceptionally fickle. Where there may be the priority of one person over another, where there'll be a fixation on the ideal kind of comfort and an unwillingness to compromise anything that could potentially threaten it. Obviously this would be further reinforced by other cards around it. But the KoP usually asks what is stability to us? And what costs are we really willing to take to achieve it.
 

nisaba

What could the King of Pentacles mean when representing a relationship/relationship outcome between two people? To me, this card is earthy, grounded, prosperous, and represents stability, material and otherwise. What's confusing is that the relationship in question is currently not that stable,

It's not about whether the PERSON is stable, it's about the relationship. Unstable people who fit well together can be completely chaotic, yet have very stable relationships.

and the two people are reconciling after not speaking for a while.

Again, that doesn't seem to matter to me all that much. Time apart can give you a sense of proportion, which can allow you to either leave for good, or settle own with someone in the longer term, having had space alone to think.

On the other, it's not a very emotional card. Thoughts?

Of course it's an emotional card! The archetypal King Pentacles loves deeply enough to provide a safety-net for his lovers and family, he is their rock, he stands as a shield between them and trouble, he is grounded and solid in their lives, he is never disloyal, he opens his "castle" to them forever.

Of course, when they get tired of him and want to leave, he's not good at letting go, because his love doesn't end when theirs does.