Spending habits are out of control

Hello friends, I recently got out of the military and while I was in service, I had a lot of disposable cash. This led to me being able to buy anything I wanted while still saving plenty of money. The savings actually happened before I ever saw the money so that I couldn't mess it up. I am now a student with a part time job making not a lot of money, but for some reason my brain hasn't put that into reality and taken it into account with my spending. I eat out instead of cooking, I order delivery, I buy silly little things that I don't need. Unexpected expenses keep surprising me; my family leaving our family phone plan and sticking me with the remaining value of 2 new phones, veterinary visits, car tires, etc. How do I get my brain to say "no I can't afford that" instead of "ahhh its ok, it'll make you happy"?? There's a ton more to this situation and I'd be happy to answer questions but I am also trying not to rant.