I am right there with you man... I was a former athlete as well and in prime condition in my 20s... you know, 20 years ago. haha
I found the motivation to make changes through support from friends, family, and my faith. It also helped going to my doctor and hearing that I had high blood pressure, was severely obese (like I didn't know that) and that if I didn't make any changes soon that my weight would catch up to me and likely kill me.
If you want to chat, want an accountability partner, anything I can do to help out, just let me know brother!