They do like to be together in groups, but two is not a group. They are a lot like discus. If you have less than 4 or 5, you will see a very pointed and direct pecking order from the dominant fish against the weaker fish. We keep them in small groups to spread out that aggression and keep it from being directed solely on one fish. This could lead that fish to get stressed and stop eating, or end up ill.
I've never had good luck keeping them in non-bonded pairs. That's why I buy six of everything now. I let it pair off naturally then sell/re-home the rest if I don't have space.