Should you be guilty about having sexual thoughts about them, particularly if you do not know if they are reciprocated?
So long as the whole thing doesn’t turn into an obsession, then fair enough. Solo masturbation is very different from expressing you sexual feeling for another while they’re in the same room. It’s purely one-sided and while not in itself a problem doesn’t give you a true perspective of your feelings towards another.
Although some people might be offended to learn that you’ve jacked off to lewd thoughts about them I would venture a fair proportion would be quite flattered. After all, don’t we all want to be wanted, platonically, amorously or sexually?
I wouldn’t suggest you go and confess all to your latest wank fantasy as a punch in the mouth often offends