sorry but if one missed birthday is all it takes for her to cut tie with him, a childhood friend of more than a decade, then she's never been his friend or a potential lover to begin with. which is fine if that's her true character is like but please stop pretending to be a friend or someone who cares for him. if there's more to the story than that then I hope the author can do it right cause as of now I can only see her as a selfish girl.
considering mc's condition he doesn't have a lot of option but even the guy who reached out to him in the first chapter and his family are much better people to spend his remaining days with. if he ever gets cured, I'd suggest to look for new 'friends' instead of hanging out with someone who would easily cut you off from her life at a moment's notice.