I have debates with myself like this all the time.
I have had someone fairly recently try to tempt me into being unfaithful to my boyfriend. Now, seeing as I don't have sexual relations with my boyfriend, resisting the temptation to have sexual relations with someone else is easy.
But where to draw the line? I do not consider a friendly hug or even a kiss on the cheek to be 'unfaithful' as such, but is there a point where even this friendly-affectionate behaviour becomes too much?