I think you've got more problems than just simply your girlfriend if you can't stop yourself lifting other peoples stuff. I think the best bet is firstly to appologise to your girlfriend explaining the situation but to be honest I wouldn't expect much.

Then I think its time to take a step back and have a look at where you stand. I'd say seek some help of someone and if possible stay clean for as long as possible including things like weed, alcohol etc.

Good luck matey, hope it all works itselft out.