In the past, you were betrayed by someone (or several someones), and it was devastating.
It hurt so badly that you're closed off to ever trusting someone again. Your trust issues won't let you engage in another close relationship.
You've shut down the part of you that longs to have a deep, intimate connection.
Maybe it was a past lover.
Maybe it was a friend. Or God forbid, it may have happened with both.
And the betrayal and pain have left you reeling.
When people you care about or love forsake you, it's natural to slink into the corner and lick your wounds for a while.
But if your pain has morphed into more deep-seated issues, and you have no trust for anyone, it's time to step back and evaluate.