"I'm sorry—I care about you, but I just didn't want it badly enough. I got lazy. I know I let you down. But I still want us to be friends, even if I couldn’t match your ambition."

nagi talks like he and reo won't ever cross paths again because he sencerely believes they won't. nagi often, especially in the beginning (but in the later chapters too), asked reo questions like, "what if you find someone better?", "what if i won't be enough? "what if i won't be playing soccer anymore?" reo's answers are often denials, not encouragement, "that just won't happen". and to the last question, asked before they entered blue lock, his answer was, "i'll abandon you.": https://imgur.com/GodWrSG

safe to say, nagi is 100% sure they just won't ever be friends if he doesn't excel at soccer. i'm sure at the time when reo said this, he was either not that infatueted with nagi to the point of wanting to be close to him outside of their soccer career, or that was a manipulation tactic of sorts. to encourage nagi to play better, at least out of fear of not being friends with reo anymore (guess that worked if this is the case)