tegi, I know how you feel. Last winter, my DS got himself a drug problem. He found a way to access an account of mine I only used for savings (so didn't look at very often) and over the course of 6-8 weeks, he stole about £800 from me. Finally, he confessed. For him that was obviously cathartic, and while he felt relieved, I was a total mess - furious, worried, stressed, bereft... He was guiltily affectionate, and I couldn't look him in the eye. I couldn't even add kisses to the end of text messages.
I was already aware of previous bits of 'ad hoc' theft - tenners and fivers and the odd quid from my purse that I was almost certain I hadn't spent. He'd always denied this, and I felt slightly crazy - not sure of my own judgement and memory. The major theft and confession couldn't be denied or ignored though - I got a locksmith to fit locks on bedroom doors, and his little bro and I have kept our valuables locked ever since. I also closed the account he'd stolen from, and changed my PINs.
It didn't feel like something I could 'punish' as such: involving the police and/or throwing him out felt more appropriate than, say, grounding. I wanted him to access counselling, but he wouldn't. I agonised over what I should do. In the end, I stopped all his allowance and changed the way he got money, so that he didn't get much, and what he did get, he had to work for. I didn't throw him out or have him arrested, and I still don't know if that was the 'right' decision.
It has been a terrible year. His behaviour got worse, in other ways. He was aggressive and occasionally violent. My love for him felt damaged, perhaps fatally. The money wasn't as important to me as the broken trust, which is still not repaired. Because of his behaviour - there have been some really big problems this year - he has felt alien and unfamiliar, and I have felt devastated by the loss of 'my' son.
However, he is growing up a bit. He hasn't stolen or been violent since Easter. He's stopped being such a dick, and it is pretty much normal teenage aggro now, as far as I can see. He's back in college.
I find I am sometimes over-sensitive. Because he has done some terrible things, and I haven't been able to stop him, I get over-wrought with smaller things, like him not coming home when he's agreed to. Even small 'misdemeanors' make me panicky, as I think "oh no, the nightmare is starting again".
I haven't quite forgiven him - and I still lock things up - but I can see that one day I might, and that is enough to be getting on with. I hope you can get to a similar point, OP. I think it just takes a long time...