How can I get through to my room-mate that he needs to take care of my things if he expects to use them?

You might mention that the things he got away with while living with his Mommy was fine, but you are not his Mommy. Grow up or ship out. Sounds like you are doing him a favour and he is taking advantage of your good nature. Get a back bone and demand some respect for yourself and your things or show him the door.