You are right that once you shoot your load, desire and excitement about it disappears. You have to get your cum into your mouth before you have any choice about taking it or not. So shooting it in your hand for licking it up after usually doesn't succeed. What you have to do is get your legs up over your head, with your cock right above your mouth, and then when you feel you are cumming, open wide and shoot it right into your throat. That's the best way to finish off, and if you're lucky your cum will be tasty and pleasant and you'll want to do it regularly.