I always liked the Stoic way looking at things (hence my Marcus Aurelius-based user name), because it was about what you can and cannot control. The past is already written, the future has yet to be written and the only story you can write in the present is your own.

I guess if I had any "easier said than done" advice, recognize that the past is in the past and focus on the present. Maybe one of your new co-workers works out regularly and is willing to take you along? Maybe (if you haven't set it up already), your new job would be willing to set aside time for a weekly therapy appointment. Perhaps a visit to your therapist before you start your new job might help?

At any rate, best of luck with your new gig!