It's way easier if you're solitary. Self-control is one thing, but mutual self-control is unheard of… Someone is going to be weaker than the other, unless you're both perfect, in which case you probably met at the gym and this doesn't apply to you. I have no relationship advice of value, so good luck with that!

You don't have the luxury that your ancestors did: if you didn't eat the gruel, you could starve. You can just go out and buy all kinds of food, and it turns out most of it is just pure calorie paste. Find a couple things you like to eat that are healthy and low calorie. Then learn to live with them. For a long time. Repetition is key to success!

Diet pills contain caffeine. Caffeine is artificial energy. You'll need it. Learn to drink coffee black. It will keep you going when you're starving.