Lucas Bergvall.

The cell phone vibrated on the table. Isa looked at the screen for a few seconds before answering.
-Hello?
—Are you Lucas?
He frowned.
—No... who's speaking?
—I'm Isadora's boyfriend.
The silence lasted only an instant.
—I found your number on his cell 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 I could answer.
That same night, Isa appeared sitting on the curb, hugging her knees while trying to hold back her tears.
"Again?" Lucas asked gently.
She nodded without looking up.
—He says he doesn't trust me anymore... that I'm sure I'm deceiving him.
Lucas sat down next to her, leaving a small space between them.
—And you?
—I'm just tired.
The wind stirred a few strands of his hair. He tucked them behind his ear almost without thinking. Isa looked up.
The kiss was short. Awkward. Impulsive.
When they separated, she closed her eyes.
—We shouldn't have done it.
Lucas swallowed and looked away.
-I know.
Isa felt a lump in her throat.
Because for the first time in a long time, a kiss had made her feel loved... and that was precisely 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).