Where did you get them from?
As for the hiding, they are extremely good at that. These guys can make themselves nearly invisible even in an empty tank.
If they stop being together it may be an indicator that you got 2 of the same sex.
I've had males getting along as long as one of them was still immature (pouch hasn't opened yet), but the moment both were mature they started fighting which usually leads to the smaller one going into hiding.
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