Oh boy. Reid can't remember the last time he talked to Jack without an undercurrent of tension running between them and part of him wants to just skip over this part of his to-do list, but you say goodbye. That's what you do, no matter how hard or how unpleasant. It's not like they'll ever see each other again, so perhaps it's even more important to settle things.
He's visibly nervous when he approaches, idly fidgeting with the sleeve of his shirt.