At some points in your life you just get to that stage where you do not feel you can trust anyone at all. Everyone has the possiblity of having an ulterior motive for asking the questions they do; and no concern seems to be genuine enough to merit you totally opening up to them incase they use it against you.
Its these times where your vulnerability lets you down; when you think you've found that one person who will completely understand; only to find that in the end they are just like everyone else; due only to the fact they are "only human" - just like everyone else.
In a world where you can only trust yourself it's very lonely. Most likely the reason people would rather get themselves hurt by opening up than keep everything bottled up and suffocate under the weight of it all.
I know that personally I love my friends a lot; but I am still shocking at keeping secrets. You tell yourself you can keep something in confidence; but the thing is when it comes down to it secrets are usually formulated around difficult or confusing situations and trying to understand them by discussing it with someone else is typical. Not because you're trying to 'rat someone out', but simply because the weight of it is too much for you to bear on your own; just as it was for the person who told you in the first place.