A virus is possible, but I also don't think that's the case because they typically don't act this way. It sounds to me like your fiancé was just feeling a little frisky and doesn't want you to know. Heh. Or, to give him the benefit of the doubt, it could simply be spam from another site. Perhaps a pop-up. Although it's the most common way, a URL doesn't have to be typed in manually for it to show up in the drop-down list.
Of course, if it'll make you feel better, it wouldn't hurt to run a virus scan.