That kind of makes sense, I mean if the object of your thinking is not married to someone else. Then it would be coveting?I know this response was 2 years ago, but it was solid and humorous. I wish you could give an "Informative" response to me, but I understand that option has been taken away.
In response to your main topic, I don't believe thinking about sex is adultery, anymore than thinking about eating is gluttony, or thinking about drinking is drunkenness, or thinking about fighting is murder. If one is more predisposed toward a particular sin, it probably pays to be alert to what thinks about and for how long, and in what capacity.
I believe the sin of lust carries with it a decision of the will - to entertain the prospect and desire or be prepared to accept the opportunity (outside of lawful limits). For example, I don't believe it is a sin to want a nice car or home, and to work toward obtaining such by lawful means. But to fantasize about obtaining the same unlawfully - e.g. by theft or fraud would not be beneficial, if not sinful. I think the same reasoning can be applied to lust.
The car, if its for sale and not belonging to someone else.
To think about eating when you are hungry, makes sense, but not if you are already full, or wanting someone else's share.
To think about drinking when you are thirsty, makes sense, but not when you are already drunk.
To think of fighting makes sense if you are in a war, or a game of boxing, or some such, but not in peaceful times and for no good reason.