Bolin got his first girlfriend when he was seven.
She was a mixed race girl, like him, but she didn't have bending to give her a side to identify with. Her skin and hair were a clear sign of the water tribe. Her eyes, on the other hand, were a dead giveaway to an Earth Kingdom background.
They met for the first time when Bolin was begging for food outside the train station. It was directly against his brother's orders; Mako wouldn't have Bolin be subjected to the cruelty of strangers. Instead, the firebender worked himself to the bone so that Bo could hide in the relative comfort of the park all day.
Unfortunately for Mako's rules, the hunger pangs were often too much for him to resist.
When he'd gone to beg that day, there was already a girl sitting under Firelord Zuko's statue. That was his favorite spot, but he didn't mind.
His seven year old self had never seen someone so beautiful.
So he told her so.
Again.
And again.
(And again).
She'd taken his hand in hers, and they'd sat there together all day. He had admired for hours how her brown fingers intertwined with his. It was all he could think about once he ran back. Mako couldn't know he was gone, but Bo wanted to tell him about it so badly.
He kept his mouth shut.
The routine went on for a few days until one day she wasn't there anymore. Eventually he found out that she'd been caught stealing food by the police.
His tears that night finally gave him away to his brother.
The relationship had done something more important than reveal to him that holding hands was fun. It taught him that if you told people the truth, they would like you.
No wonder Bolin had so many friends.