Do guys really undress girls with their eyes and imagine how they smell?

I was just wondering because I saw this on a show, like dr. phil or something. && I asked my boyfriend and he says he neverrrr does that. swear up and down I'm the only one he wants to look at. but for some reason I think its bs and I don't believe him. so jw if their is any other guy that has a girlfriend , or doesn't, and doesn't undress girls with their eyes or if its an every guy thing.?
Do guys really undress girls with their eyes and imagine how they smell?
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