i had a pair of pearl gouramis, of which the female died a few months ago, they had been together 2 yrs.the male had the same symptoms as yours hid away , nothing really wrong , just miserable, when we got a couple of mollies he seemed to be taken with them as they were a reasonable size and all the other fish were small. we are now looking for another female , about his size, he may get rough with asmall one, .give it time , he may get over it ,you didn' say if he was one of a pair.. if he was you may need to give him a grieving period and get him another friend, if he wasn't then hopefully he'll get over it and find another friend... hope it works out ok jackie