My motivation comes from misery tbh. When I gain weight I don't feel like myself. My attitude completely changes. I don't get dressed up anymore, I don't go out. I don't like wasting my life away so I do what I know will fix what makes me miserable, which is lose weight and keep it off so I don't have to keep starting from the beginning every time.
When it comes to the eating healthy, start off slow. Don't take on a whole bunch of diets and make lots of drastic changes all at once. You'll be overwhelmed and be more inclined to drop everything.
Make minor changes. Add a lot of healthy veggies and fruits to your normal, everyday diet. You'll start realizing you get full much quicker when you start adding them, making it easier to cut out some of the unhealthier foods. Switch from dairy milk to almond milk. A candy bar/pint of ice cream a week instead of binging on em. From corn to olive oil. Try baking things instead of frying them. Switch bottled salad dressing for your own homemade vinaigrette. Small things like that. Then, when you manage that and it feels easy, make bigger changes. Brown rice instead of white. Cutting out fast food altogether. Taking smaller steps instead of big steps will insure success because you're not forcing yourself to get used to too much at once. Good luck!