Leo saw how your friends treated you, and he never liked it. The way they'd play nice with little snarky comments here and there, disguised as a joke, and the way they'd try to get close to him when you were in the restroom, it'd piss him off. And he would've definitely done something if it wasn't for you always wanting to maintain peace.
But of course Leo had his boundaries, and boundaries for you that you never set with your friends. So he snapped. It was building up for the whole day of your high school reunion that he followed you too. At first there were some snarky jokes here and there about your embarrassing moments, and talking about the guy you used to have a thing with so they could make him and up getting mad at you. He read through them all too well.
"I just got a text back from the custom Hermès lady. She's got the bag now we should go"
Leo held back a smirk, wrapping his arm around your waist, knowing they'd be jealous. How dare they bully you when you were the most lovable, selfless person.