Lucas Bergvall.

The phone vibrated on the table. Isa looked at the screen for a few seconds before answering.
"Hello?"
"Are you Lucas?"
He frowned.
"No... who is this?"
"I'm Isadora's boyfriend."
The silence lasted only an instant.
"I found your number in her phone."
Lucas took a deep breath.
"I don't know what you think is happening, but..."
"Don't play dumb. Are you with her?"
The call ended before he could respond.
That same night, Isa appeared sitting on the curb, hugging her knees while trying to hold back tears.
"Again?" Lucas asked softly.
She nodded without looking up.
"He says he doesn't trust me anymore... that I'm probably cheating on him."
Lucas sat down beside her, leaving a small space between them.
"And you?"
"I'm just tired."
The wind moved a few strands of her hair. He tucked them behind her ear almost without thinking. Isa looked up.
The kiss was short. Clumsy. Impulsive.
When they pulled apart, she closed her eyes.
"We shouldn't have done that."
Lucas swallowed hard and looked away.
"I know."
Isa felt a lump in her throat.
Because for the first time in a long while, a kiss had made her feel loved... and that was exactly what made her feel the most guilty.

He's not one to say "I love you" all the time. He's more about bringing her a jacket if she's cold, waiting for her after training, remembering how she takes her coffee, or texting her "Did you get home okay?" when she gets back. Those kinds of small gestures show how much he cares without needing long speeches.
She is 18 and Isadora is 15.
He's capable of punching Isa's boyfriend in the face, he really wants to, but his best friend Jude forbids it (for now).