Thieves never change, once a thief always a thief. Fact is he did it to a friend of yours that you yourself confirmed... TBH its pretty dumb of you to even have him over to your house again... especially unsupervised enough to have the time to steal something.
With that being said, yeah he might have a problem... not like a clepto problem, but if the dude has a job and is still stealing things to sell them... well its more than likely drugs or gambling. You might want to help your friend, you might have tried, but you cant change someone who doesn't want to change. Aside from that if it is a drug problem, one of the first things they teach you in rehab is to cut all former ties... so even if you help him you're relationship is going to end.
Ditch this clown and find a friend who isn't a thief.
“What I say is, a town isn't a town without a bookstore. It may call itself a town, but unless it's got a bookstore it knows it's not fooling a soul.” - Neil Gaiman
