Im with nodose on this one, the deer just feels a thump and hears a loud bang and runs like satan himself is chasing it. And just because you tracked for 45 min dosent mean the deer took that long to die, if you made a good shoulder shot as you say he didnt suffer so dont worry about it and keep on hunting as long as you feel like you want. There some people who just cant kill something else intentionaly. My grandpa couldnt be he was just as happy as ever for me when i got a deer. So dont feel guilty.