another thing I'll add to this.
The mature reasonable thing for him to do is not message me some single sentence of self deprecation in the hopes of getting pity. He should have formulated an intelligent longer form message both admitting to and recognizing his mistakes while also giving me a clear plan. This plan should have included generally what things he was going to do to improve his fitness, how he was going to keep himself accountable, and what his end goal fitness wise is. He didn't even say "hey alan I am gonna do whatever Johnny tells me to so that I will run a 9 minute mile and be able to do the other fitness standards by the spring, and I'm gonna make sure he checks in on me multiple times a week to keep me on track."

Recognizing you have a problem is the first step, but if thats all you do then you might as well have done nothing.