I personally think that your friend's 'life viewpoint' will contaminate the game to the point that it will not be fun for one or the other of you. He appears to have alot of 'personal baggage' upon his shoulders.
That said, some ideas. Do the campaign as a quasi-morality play.
'If you don't manage life, life manages you' - have encounters and events occur that require his character to deal with. If he choses not to deal with the issue, have a consequence impact his life. Show him that he will have far better outcomes if he is more proactive in dealing with issues. Perhaps this will get him to come out of his shell more.
'You can't hide from your problems, they eventually catch up to you' - let's face it, your friend is trying to hide from his problems and thus, so is the character. Alias, unless one confronts and deals with one's problems, they remain - and sometimes get worse.
So, if his character doesn't want to deal with humans, have humans keep showup - and they are not going away. His character must now interact with them. If he ignores the wood cutter, the wood cutter starts cutting trees in his area. If he continues to ignore the woodcutter, then more trees are eventually cut down.
'If you are not part of the solution, then you are part of the problem' - have enounters and events that require him to be part of the solution. If he refuses to rise to the occasion, make him part of the problem. Using our old friend the woodcutter example - if he ignores the woodcutter, then the druid gives him a hard time about why he isn't doing more to protect the trees or educate the woodcutter about how to avoid clear cutting trees and planting a tree for every tree cut down.
Some ideas. Through a quasi-morality play approach, perhaps the character learns to be less an isolationist and more proactive and social. And perhaps, just perhaps, the person playing the character learns something to apply in his own life.
