First, let me say congratulations to you on a very impressive accomplishment. Twenty months is great.
As for how long will the urges continue?? Your question reminded me of something. I was at my grand-fathers 90th birthday party, one of his sons playfully asked him "At what age do you stop noticing the pretty girls" without missing a beat he replied "you have to ask someone a lot older than me".
Point being, I think this will always be with us to some degree. Not much different than the alcoholic.