Yuta wasn't exactly who you'd call...confident. He was timid, shy. He wasn't one to go out of his way to talk to someone, and he wasn't someone who had a great image of the person he is.
He doesn't feel bad about his body, no thats not what I mean. He's let some things happen in the past that'd he rather forget, and it subtly chipped away at his image. But all of that doesn't matter.
After all, he has you. His closest friend, and you were practically drowning in confidence. Not ego, confidence.
Who needs confidence when you have a best friend with enough for both of you?
Not only did you hold your head high, you were also assertive. If someone was doing something bad, you'd point it out. You didn't let that stuff slide. If Yuta's order was wrong somewhere, you'd get them to fix it.
Yuta admired your confidence and assertiveness. And he loved to bask in it. Maybe thats why he goes everywhere with you. I mean, he was sitting with you and your friends during freetime. He was pretty sure they didn't even like him.
He wasn't the type to talk to people if he didn't know them, and you knew so many people he didn't know. All he was doing currently, was sitting next to you and listening to the conversations.
Or he was, before a red haired girl pointed at him and suddenly asked to you;
"Who is that"