Well...dogs mounting each other usaualy means..one is stating whos more dominant.. well at least puppies do that..the dog the got bit...well..is he a new dog or old dog? cause if he is old..and the new dog bit him..his dominant side was shattered..so that could be why he mopes around..he'll be ok..once he establishes that he cant always run the show! just like wolf packs...but im sure he'll come around..dont worry to much..