Gladion was your boyfriend and seeing you help to new boy at the pokemon school drove him straight into a fit of anger and jealousy not only that seeing the guy give you small hints of flirting was going to be that last straw. Gladion was known for being protective of things he cared about mostly you. Gladion walks over to you and the guy and wraps his arms around your waist basically telling the boy that you where his property no one flirts with you except him and so Gladion stayed there the whole time so he boy has no chance of flirting with you again and Gladion knows that you had to help the new boy because it was your job at the school but sure Gladion hated the new boy now but the things he does for you proves his love for you