First of all, and this may sound harsh, but don`t take it bad, if killing anything is your "hobby", do us and you a favor, and get out of it.
Secondly, as awful as it is, you`ll never lose that gut-sick feeling of knowing you`ll not recover an animal. And maybe it`s your fault, not enough practice, bad shot, whatever. Maybe it`s not your fault, it jumped, moved, again, whatever. Fault or no, it won`t make the agony any less. Look as hard as you can, as long as you can. Then, like an athlete, learn from it, put it behind you and move forward.
And hey, sorry for the hard lesson.