My boyfriend doesn't want to have anal sex anymore?

My boyfriend and I had anal sex about a month ago- and haven't since. He used to love thinking about it, and was so excited to finally try it, but when we actually did it he got feces on his penis (it was both our first time doing anal, I really should have prepared more) and it seems to have turned him off for good. I still want to do anal, what should I do to make him want to have another go at it?