Betrayal: You were personally betrayed by someone very close and dear to you causing your great heartache. (Work with your DM to detirmine the details)
Pickpocket: During your adolescence your family fell on hard times forcing you to turn to petty theft and other criminal activities involving you with criminal organisations.
In adulthood you have an encounter with an unusual person, who as far as you can tell, has no home or family. You offer to help in anyway you can. After accepting your hospitality the stranger vanishes leaving a note "Your kindness will be remembered".