UK Girl, make some new friends you can trust and respect. Replace the thief with people who are worthy of your friendship. I'm being blunt about this, but it comes from my personal experience. When I was younger, I would give unreliable people whatever they would take, thinking they needed my help. I would keep giving them second and third chances to "change", and it just made them continue with worse behavior than before. It resulted in them continuing their bad behavior and me being exploited. There are lots of good people around to be friends with. There are good people who do need help in this world who will not take unfair advantage of your kindness. If you spend your energy on people who will appreciate help, you will be rewarded, not exploited.