In my experience no human is ok with being socially isolated for a long period of time. But difficulty with forming healthy social relationships makes the experience of attempting to "warm up" to others very unpleasant to people who don't get social exposure to begin with. Especially for anyone that performs extensive introspection it is very difficult and the experience can be interpreted as unhappiness.

I think maybe being with others is most pleasant when one has a healthy relationship with one's self.