reading your ad now and he sounds like a blast. cassie is competitive in the blandest way possible. her philosophy is that if she performs to her personal standards, she can accomplish anything. doing well is the expectation, it doesn't make someone exceptional. if he's more the charming braggart type, it would confuse/infuriate her.
specifically, she could use an ex who knows her secret (online she goes by 'venus' and writes smut about the paladin crew) and uses it to extort little things like free drinks and dry cleaning. more staff or spies feeding her info to use in dumb ways. but if they wind up just being cadets together, that's grounds for plenty of interaction and i'm always game for crazy organic developments!