But what would you do, back-stab yours right in front of him?
Just to add a little comic relief, you can't stab him in the back with him standing next to you....[8D]
Anyway, to answer that question.....HELL YES!!! Without hesitation! First, no friend of mine best ever put me in that situation to begin with. I sure wouldn't them.....Second, it's a dog eat dog world out there. Eat, or be eaten. When it comes down to me or "you" (not specifically you, but you understand...) It ain't gonna be me!!
Friends are friends.....and we do what we can for each other, but there are lines and limits. Both were crossed in this case, IMO. This is just me, and by no means advice, but that would be the last time I spoke w/ that "friend."
Cut your losses and run. Pay the piper, and don't make it worse than it is. IMO, you knew he was illegal and went anyway, which makes you an accessory. If you didn't know, that may be a different situation, but you did. I'm not sure about where you live, but poaching deer in MO carries w/ it some pretty stiff penalties, if you catch my drift.