I think he gets over it like the pain and starts all over may-be
I know this is an old comment, but other people might have the same question: A lot of times, especially with high schoolers who are young and impetuous, the desire to quit after an injury is there because you can't do what you used to be able to at the level you used to be able, and it's very, *VERY* frustrating. What Rui's probably done, now that his friend has reminded him that he wants to, is re-joined in an injured capacity. He can still help, coach, and do some drills, not to mention hang out with his friends. He's probably still doing rehab and wont be a starter anytime soon, but it's not black and white. He still has options.
I didn't really understand the end xD wasnt he injured and couldnt play anymore? Why does he play again? Or was it just for a time that he couldnt play and after his rehabilition he actually can play again, but then isnt it somewhat strange that the maincharakter quit baseball, i mean his friend surely would have come back or not? I'm really confused here xD