It's because Dean thinks the best of him that he's found it hard to say anything. The proof is in the confusion Dean looks at him with. Sam eyes the pro-offered beer, contemplates taking a sip to make things easier, but even he knows in Heaven, everything is more or less a placebo. What he ends up doing is he partially hangs his head until he pulls it back up, takes a sharp intake of air with his tongue between his lips and pulls them thin. He takes his time. 

For Dean to understand, he figures he should start at the beginning. "You know how Jack is working on helping innocent souls that landed up in Purgatory and bring them here. Garth, his wife, his children aren't the only ones that ended up in recently." He scrubs his forehead.

"I...ran into Madison a while back. At first she was confused and traumatized and not able to speak much. But right away she was able to recognize me. My first thought was that I had to help her. Really, I didn't help anyone." He says with all the stops and stutters of telling a heavy truth.