While happiness doesn't guarantee success, it sure has hell makes it easier to work hard!
The darkest year of my life was sophomore year in college. I wasn't doing well in my classes, so I dropped some hobbies to make more time to study. I got out of shape, gained weight, lost touch w/ my friends, put more pressure on myself to make all of these sacrifices "worth it," and welp – my grades never improved.
The next year, I fell in love w/ this boy.
After what most people call a downward spiral, I essentially fell straight into an upward spiral! Falling in love was (and still is)... inspiring. I got back into shape, rejoined all of the teams and activities I had quit, and also got straight A's in not four, not five, but all six of my classes (at MIT).
Being happy doesn't magically transport you to the finish line, but it certainly makes running the race more enjoyable. As the quote says, happiness is indeed fuel.
And lastly, I don't know if you're proud of yourself for losing so much weight, but you ought to be! When I get out of shape, my goal usually starts out as "I want to feel good in my body." But every time I start the process (and it happens frequently because I'm a bit of a yo-yo-er), I start to get really geeked by the progress. Progress is one of the only things that reliably and consistently makes me happy. (It's the best!!!)
My experience is that if you rely on progress for your emotional wellbeing you will not have a good time. Progress too easily slips backwards or plateaus for long periods of time. It sounds like the kind of ting someone would say during the easy beginning stages of of a thing.