Take his wallet with all credit cards away from him, remove all laptop chargers and PC power chords. He will have lots of trouble and hassle to replace those, and then you can just do it again.
And don't listen to your mom. Allow me to be straightforward. People are weak and do stupid things when under emotional pressure. And she is under enormous pressure. She will tell you to fix things for your dad. Don't. My advice is as such because I went through something similar.
I had to be very rough to both my parents when they divorced. They both did huge mistakes just because they were mad at random things. My mother was so depressed, she decided not to ever work again. She kept saying she was too old (43? lolwut?) to find a good job, that no1 needed her anymore. She wanted to pass by on savings until I graduate and work to support both of us.
She also decided to bring action in court against my father so she could get as much cash as possible out of him. I hid property allowances for our countryhouse just so my Mom couldn't go to fight for it in court. Without the papers, she wouldn't be able to prove 50% of it belonged to her. She wanted to sell it and get the money just so she could keep being unemployed and live on savings.
I took her driving license and reported her to police when she took off to the pension fund to withdraw savings. She got stopped by police and had her car taken away for 2 weeks. And I knew she is the kind of person who would rather choke herself, but would never take a cab or walk.
When she asked me to help with a cash deposit, we both went to the bank, and I played it so the account was on my name, so she couldn't withdraw the money whenever she wanted to. She ran out of accessible savings money 8 months and had to look for a proper job. Without an urgent drive to do so, she would've never do that. I know she wanted just to wait for me to graduate and find a job, and support us both, while she does nothing. Awesome plan, except for that completely ruined my masters degree prospects and any chance to move out and live together with gf.
It's been 3 years now, and she is doing fine. So am I. I do regret some of my actions and decisions had to be taken, but I think it was necessary. I was 19 then, just like you.
Lesson from that? You have to be very tough. These family shenanigans take a lot of willpower to pull off. It is especially painful, because it's your parents, the closest people you will ever have. It's only your call. People don't fix their own shit. Unless you take direct and focused action, change will never occur. I learned it very hard way when I left for college abroad at age of 15. Now, 7 years later, everything I had to do seems so obvious and simple, but at the moment the choice had to be made - very tough decisions. Stop thinking, start doing things.
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