You don't have to say anything! Body language can be a deal breaker. Put yourself in their shoes as best you can, be genuine and heartfelt. So don't see them if you're not in the mood; they need you at your best and truest.
If you're on your phone a lot in front of them when you're supposed to be catching up or visiting to give support - do exactly that. Disconnect from your world and change the distraught person's world, even if for a few minutes. Lend an arm to lean on, leave them an unexpected meal such as dinner or dessert, and check up on them. Even just a hi, i've been thinking of you.