Et Tu, Brute?

This is a contest entry from cmara: https://www.deviantart.com/cmara/journal/TV-Tropes-A-Z-912910452

Trope used: https://tvtropes.org/pmwiki/pmwiki.php/Main/EtTuBrute

So I got this headcanon/AU story where Thomas found out Diesel was a false friend of his all along after one of his sabotages had gone too far and almost killed his best friend Percy and he didn't have any remorse on Percy's near death experience so Thomas called him out for never care about his best friend almost dying and called off his friendship with him.