Coworker question

my co worker and I spent the summer getting pretty close. Some of our coworkers think we’re dating, all of them think we like each other a lot - when he’s in the office he’s constantly at my desk, he even joined my sand volleyball team this summer. He’s always finding reasons to be at my desk or in the same places I am. Unfortunately, he put in his two weeks and is leaving our company. I don’t have the guts to ask him out (and that won’t change), but I have told him I don’t want him time leave, he’s also told me he doesn’t want to leave bc he likes working here. I’ve always gone by the rule of - if a guy wants to ask a girl out, he will. Am I wrong? When he’s leaves - if he wants to keep seeing/talking to me - at any capacity, he’ll say something, right?