what would he have to do to prove he's worth giving another chance?

Met the most amazing guy 3 months ago, things were so good but he just couldn't commit at the time due to personal circumstances, here we are about 3 weeks later, he wants to try again, I've made it clear that he really needs to prove himself in order for me to give him a second chance however I'm not sure what would be enough as I really want us to be together, things were so perfect but I obviously needs some type of reassurance that he's not just going to turn around and tell me he's not ready. How much can really change in 3 weeks?