I also do HIIT and Spin class twice a week. One day a week I do the elliptical just be be alone and relax with my music. I have maintained my weight. I never thought I would love the gym but once I joined it became a big part of my life. :0(
As a kid, I was an all-star athlete who got straight As and had visions of becoming a MLB player...but life interceded and gave me a different path.
When I completed my MBA at 37 as a single dad with 2 young daughters, I gave myself a fitness club membership as a reward and have belonged to one ever since.
Like you said, it truly becomes a lifestyle.