Tricky one, here, for me. I have mega-social anxiety, and am also solitary by nature. I like to go out to concerts, films, galleries but always prefer to do these things alone, quite apart from the fact that I have no friends and none of my family share my tastes. I never talk to anybody when I am out if I can help it, indeed I get profoundly irritated by the people around me, especially at concerts. It's not uncommon for me to leave a concert early because I can't stand the people around me any longer. People shouting and dancing and drinking and shoving. People talking and fidgeting and coming into my space. Drives me nuts and often completely spoils my enjoyment of the music. A couple of years ago I even left a concert I had been looking forward to before it even started as the people around me were chatting and laughing non-stop, which annoyed me terribly.
So, aloneness is my chosen state and my natural condition.
Isolation, to me, means something more profound than that - a loss of contact with the momentum of life, a poverty of purpose and reason, a feeling of not knowing who I am in relation to the social and material world around me and of having no control.
I've always been alone by preference, but only periodically do I exist in the barren cold of isolation.