I never open up to anyone, not even my parents (which annoys them greatly).
Though I don't keep secrets if they are mine, if someone asks I will answer truthfully (granted they have to know what to ask for, a vague question gets a vague response). Secrets given to me are perfectly safe though, mostly because I can never gain more than I lose by revealing (trust is important in my line of work and social status)
Edit* I am much more likely now adays to confront almost anyone, the whole loner thing is dreadfully lonely and boring. I'd much rather try my chances meeting everyone, you can't make friends unless the first hello is initiated.