((((((hugs)))))))
You are one of the most compassionate, caring people I know, of course this wasn't your fault. And Delta may well be doing fine on his own, try to envision him curled up snoozing peacefully, or standing on a rock, looking around. You might see him again, you don't know that anything bad has happened for sure. All you do know is that he's on his own right now. He probably doesn't think he's "lost." I'll keep praying for his return, of course, and that you can find some peace of mind.