One possible reason could be to protect himself from the pain and loss he has endured. After all he's been through, like the death of his parents, Sirius, and so many others, turning off his emotions might seem like a way to avoid further hurt.
Ron, on the other hand, might feel a bit betrayed. He's always been close to Harry on an emotional level, and seeing Harry turn off his emotions could make him think that Harry doesn't care about their friendship as much anymore. But in the long run, they would probably try to find a way to bring Harry back to his normal self.
It could also be related to his self - preservation in the wizarding society. In a world full of magic and danger, showing too much emotion might be seen as a weakness. Harry, being aware of this, decides to shut out his emotions to appear stronger. He has faced a lot of scrutiny and jealousy from some students and even some adults in the wizarding world. By suppressing his emotions, he hopes to be more respected and less of a target.
In terms of his romantic relationships, if there are any in the fanfiction, it could be a major obstacle. Shutting out emotions means he may not be able to fully open up to a potential partner. This lack of emotional availability can make it difficult for the relationship to develop. For example, if he has feelings for Ginny, his inability to express his emotions might make Ginny feel unwanted or unloved, even though Harry might actually care deeply.
Hermione and Ron would surely be his first allies. They have always been by his side through thick and thin. Also, Luna Lovegood might be an ally. She has an open - minded and accepting nature, and she would probably see Harry as still being the same person despite his new form.
Ron would probably be both shocked and a bit awestruck at first. He might make some typical Ron - like jokes to ease the tension, like 'Blimey, Harry, you're a dragon! At least you'll be good for scaring off Snape now!'. But deep down, he'd be worried and determined to help Harry get back to normal.
His friends would be quite shocked. Neville might be a bit scared at first, thinking it's some new dark magic. But then they'd all come together. Ginny would probably be the one to try and comfort 'cat - Harry' by giving him some fish or milk, thinking that's what cats like. And they'd all be determined to get him back to normal as soon as possible.
His character development would likely be very different. Instead of growing through emotional experiences like the loss of loved ones or the joy of friendship, he would develop in a more cold, calculated way. Maybe he'd become a master of spells not because he has a passion for magic, but because it's a means to an end.
His friends might be initially terrified. Hermione, for example, would be both scared and immediately start researching how to reverse it. Ron would probably be more shocked and not know how to react at first. Their friendship would be tested as they try to figure out what to do. They might have to keep Harry's transformation a secret from other students to protect him from being hunted or experimented on.
Well, it could enhance his friendships. For example, he'd be able to tell when Ron or Hermione were feeling down and offer immediate comfort. It might also make his enemies more wary of him, as he could sense their malicious intents. He could use this ability to his advantage in the wizarding battles, being able to anticipate his opponents' moves based on their emotions.