Lost my identity as an athlete after becoming a dad
Used to run marathons, played in a competitive basketball league, spent hours at the gym. That was my thing, you know? After my first son was born I told myself I'd get back to it. Now he's 5 and I'm just starting to get back to running but only 20 minutes here and there at 5:30 AM. I'll never be that guy again and some days I grieve it. On the flip side I've found new purpose I didn't expect. The kid watches me run now and wants to run with me. We do a mile together sometimes and he's so proud. I guess I traded one identity for another.
The gym hours are gone but you haven't lost your identity, you've just expanded it. Being a dad IS part of your identity now and that's not a bad thing. You might surprise yourself with how much you can still do.