The Past Haunts Us

"A good spy knows how to read other people's emotions. So when he saw MacCready crouching by a corpse of one of the many Feral Ghouls he and the crew had killed to clear Fiddler's Green Trailer Estates, he knew something was wrong."
/or/
When Deacon, MacCready and the Sole Survivor Nate headed out and MacCready didn't feel so good.

Deacon/MacCready