Xavier is Frank's editor, he's the guy in basically every Frank video that has his face blurred out. He's the guy who was in Gamer Nighmare blowing vape smoke at the D&D players.
Frank was only involved with the wiggers because he's Sam's friend, he was introduced to MDE people because he trolled a news station after a shooting and namedropped Sam Hyde and GamerGate(Xavier was also DeagleNation)
The second Sam stopped being involved they snaked Frank over his (valid) criticisms about the s1 edit being shitty and cutting him out. Jet is a huge fag for that. The underlying reason also is probably that Jet is doing the thing everyone who gets a little clout and starts egofagging does and not wanting to work with people who aren't totally subservient to him
Frank is notoriously hard to work with because he doesn't really have an Off-Switch and is liable to crash out on his own editors and collaborators, which is why he's so locked in with Jace(because they're good friends unrelated to content creation)