Existential exercise habit questions from a long-time lurker

Hi friends!

I've struggled with/been highly aware of my weight since I hid puberty. I've read multiple sources suggesting that diet may be more important than exercise in weight loss, but I'm a student who lives a pretty sedentary life and have to think that exercise makes a real difference. My trouble is how much I truly hate exercising!

The thing is, I used to be a fairly high level athlete and even then, I never enjoyed it. I'd be swimming 2-4 hrs every day in middle and high school and LOVED when I didn't have to exercise. I've never experienced that feeling of being unhappy w/o exercise; moreover, after I do I'm just tired and grouchy.

I'm at university now and having decided not to pursue collegiate athletics, I've gained quite a bit of weight and have so much trouble motivating myself to work out.

TL;DR I don't get thing so-called "runner's high" after working out and never have. Do other people feel that way?