Diarmuid almost lets Reno go. Considering how badly his attempts to help have gone so far, it seems like the wiser thing to do before he causes damage he can't undo. Perhaps someone else can get through to him where Diarmuid himself has not.

But...it just feels wrong. Where would Diarmuid be if Waver had given up on him when the magus didn't understand or was worried about hurting him? Would Diarmuid even be recognizable?

In the end, he can't do it. Diarmuid can't just let Reno walk away. Decision made, only a heartbeat later, he is standing in front of the red head, hand clenching the man's collar so that he can't continue forward.

"Why are you so determined to run away today? It won't get you anywhere," his expression is sincere and worried. "Believe me, I know."