Hi Binky!
I might be way off base here but I'm saying this based on what your post sounds like to me.
I think you might be looking at this too much as "going on a diet"...meaning, at some point, you're gonna come off the diet, like what happened after the low-carb diet, I'm assuming? Have you replaced your favorite fast foods with other things you like that are better choices? You didn't say anything about what you're eating now.
I understand the "last meal" ritual. I did something similar, although not so restrictive. I had decided January 1 was going to be my changeover day. December 31, my mom and I went to a restaurant and I had a slice of cheesecake for dessert, knowing not that I was never going to have it again, but that I was simply going to be a little more careful from now on. It was more like me symbolically saying to all my fattening foods, I'm gonna be monitoring things a little more closely from now on so I probably won't see as much of you as before.
That basic eat less, exercise more approach is what's been working for me so far.
I think the best advice I could give, based on what's working for me and what I've seen other members here say is:
1) Approach it with a mindset of it being a lifestyle change, a routine change, not as a diet meant to last only until the weight all comes off.
2) Start creating a new normal. You don't have to go cold turkey (pardon the pun) or cut yourself off from everything you like right away. Make some changes, even if they are small ones, and see if you can live with those, before tackling more changes. If you find yourself angry, frustrated, upset or deprived by whatever plan you're on, then that may not be the right one for you. The key is adapting, not forcing.
3) Move. Shake your booty. Exercise. Again, you don't have to walk or jog a mile today. Find some exercises you can do, even if you can only do them 10 minutes at a time. And make it fun for yourself.
4) Break down your goals and the weight-loss process into steps. Don't focus on losing 140 pounds. Think about the first 5-10. That's a more quickly accomplished goal. When you've done it, you can focus on the next 10, knowing that if you did it once, you can do it again.
Don't make yourself feel like you are walking the green mile to death row. Think of it more like the yellow brick road to a really cool place.
Okay, I could really milk this Wizard of Oz metaphor here but I'll stop now, lol.