I wonder if your colleague actually has those thought running through his head at most times, even the good ones, but when he's busy he doesn't notice them as much.
This is what I imagine - but they keep themselves busy. However, they did say that normally they are quite positive and optimistic.
I believe that the best "cure" for loneliness is to enjoy your own company.
Oh for sure! However, I think that this is also impacted by the state of the current conditions. When things are good, people tend to say that they are happy to be alone, but that is probably because their head space is positive too. When things turn though, that darkness arrives.
It might be a good time to toot a little, but I will give it some space first, to see what other fires arise :)