I completely love to do the same. I've not always been able to get it up when I've wanted, esp. if the scene just isn't right, but once I've gotten it up and shot my load, I won't loose an erection fast. So I usually take that time to please the bottom a bit buy fucking him more, creaming my load in his ass. And from time to time, I get so aroused fucking with my own cum as lube, that I even shoot another load after that.