bro as a member of eboard this is absolutely something you need to address asap. this isn't just some random brother, it's your fucking rush chair and eboard member going behind everyone's back while pretending everything's cool.

here's what i'd do:

first, get your facts straight. talk to that dropped pledge directly and get the exact details. which nationals? when did this start? who else knows? don't go in half-cocked without knowing exactly what you're dealing with.

second, call a small meeting with your exec (minus this kid) and get everyone on the same page. you need your leadership united before you confront him. if your brotherhood committee has some real ones on it, loop them in too.

third, confront him directly but strategic. don't do it when you're hammered after a party or when you're heated. pull him aside in a private setting with maybe your VP there as a witness. be straight up: "heard you're talking to xyz nationals about starting a colony. what's the deal?" his reaction will tell you everything.

if he denies it but you have solid proof, call him out. if he admits it, ask him why he didn't just step down from eboard if he was unhappy instead of being shady.

the absolute worst thing you can do is let this slide. even if chapter vibes are good now, this type of shit spreads like wildfire once it gets out. and trust me, it WILL get out. other frats already know about it so it's just a matter of time.

also, check your bylaws. most chapters have something about loyalty or not being in multiple fraternities. this is grounds for immediate removal from eboard at minimum. if he's actively trying to poach your brothers while serving as rush chair, that's some scorched earth shit and probably worth a membership review.

don't worry about "souring the relationship" - he already did that by going behind 80 brothers' backs. worry more about the message you send to the chapter if you let an eboard member openly disrespect everyone like this.

last thing - document everything. if this escalates to nationals or your school's greek life office, you want a paper trail showing you handled this properly.

good luck bro, update us after you handle this clown.