Jackson never gets mad, he's not the type to be butthurt and holding grudges, he doesn't get angry or aggressive and still he's balling his hands into fists at this very moment, eyes glaring at Mark with anger and pain and more than those it's the sadness in his eyes that has Mark's stomach turn and his windpipe tighten.
He wishes he could take it back, erase the words he mindlessly dropped from his lips because he thought he could, because he believed that Jackson would understand what he's trying to say but it seems like he never got across what he tried to convert to his friend and now that term seems to no longer refer to them.
It could have been taken as a joke if Mark hadn't voiced it with conviction, Jackson would have laughed and Mark would have felt the boy's halfhearted punch against his shoulder and then an arm wrapping around his shoulder and they could have stayed friends and moved on.

Right now the sadness reflecting from Jackson's features, the downward tilt of his lips and the knit in his eyebrows, the way he clenches his teeth and forces his arms to his sides shows that there's no taking back the thing he said.
It's not done with “I'm sorry”, there's no chance for “Let's forget about it” to fix it all because Jackson feels betrayed, he's hurt and maybe if Mark hadn't kissed him along with the confession it would've been half as destructive but when he decided to tell his best friend that he loved him he never imagined he'd end up picking the shattered pieced of their friendship off the floor.
Now it's too late to make it all undone and the only thought that occupies Mark's mind is that he hopes Jackson will give him a chance to fix them back together.