Rehome or keep

Hello! Im really having a dilemma here with my eastern box turtle. He was wild caught as far as I know (he was gifted to me when I was five). Throughout the years, I have done my best to care for him properly, but being given him so young, I had some deficits. He’s been indoor all these years, save for walks around the yard. Ive now had him for nearly 18 years, and I am currently away from him as he lives with my parents while I’m in college. I am moving this year and plan to take him with me, but I will be in an apartment, so there is no way for him to he converted to outdoor.

I love him, but I know box turtles do not thrive indoors, regardless of space. I know the ideal is to have never kept him at all, and release him back to his range; but I cannot change the past. I want the best for him, and I just need advice. Should I attempt to rehome him to someone who can give him an outdoor enclosure? Give him to a sanctuary or rescue? Or keep him and attempt to free roam him/giant enclosure? I want to atone for the care I’ve given him throughout the years, especially in my childhood. As much as it hurts my heart to think of giving him away, I want him to have the happiest life he can.