You know, that's sort of like when I beat off with the intention of eating it. I cum but almost always lose the desire to do it. Same with what you asked about. I have often thought it would be erotic as all get out, but after she finishes me that desire goes away as well. I did once ask her to let it all drip out of her mouth and let it flow down my cock. She did, and then she licked it off. Not nearly the same thing, but pretty damn cool. They only other variation we ever did was after she went down on me and I was nearing my climax, she had me finish myself off by masturbating (she has often done that, but she has me in her mouth when I finish the job), but she pulled her mouth off of me and watched me cum - then she licked that mess up with her tongue.