Okay, so you've killed your horse... cheer up. Also, the co-op in Red Dead Redemption is slightly underwhelming. Cheer up again. We've just been told this by Rockstar.
"Today we’re happy to announce that the ‘Outlaws To The End Co-Op Mission Pack’ for Red Dead Redemption will be available for download on June 22 for both Xbox Live and PlayStation Network. This exciting new content will be free to download and includes six brand-new co-op missions, as well as new co-op challenges, bonus multiplayer XP rewards, and extra opportunities to unlock additional Achievements and Trophies."
There you go.