despite my distaste for the way their relationship played out, there's no denying that jounouchi is a huge part of mai's life and a huge factor in her motivation and dedication to truly finding herself (which makes complete sense, considering how openly selfless and unconditionally caring he is).
jounouchi has a personality that is completely outside of mai's range of experience-- she's never met a person like him before. she's never before been treated the way that he treats her.
because of that, mai instinctively feels like she needs to protect him-- he is such a one-in-a-million kind of person, he has so much goodness, and she finds purpose in protecting him and making sure that he's okay. she becomes angry and acts recklessly when he's in danger or is hurt, and she gets pissed as all hell when she sees that he's out of spirits.
when she loses him during her duel with malik, she isn't just sad and lonely, she's scared. if she can't remember him, she can't be there for him. she can't protect him anymore, and in that, she loses a purpose. mai's life isn't centered around jounouchi, he isn't her single purpose, but his role in her life-- the safety and motivation that she gets from him and his friends, is something she can't lose. he is irreplaceable, his goodness is irreplaceable, and she doesn't expect to meet another person like him for the rest of her life.
