If you have committed adultry/infidelity: Did the 'new' relationship start as a friendship (platonic)?

Curious to now how many 'cheaters' out there didn't intentially start out that way. Did your cheating relationship start out as just casual friends and then develop into a deeper (ual) relationship? What were your first signs of knowing that the friendship was becoming something more (prior to ). How did you change towards your spuse during that time (e.g. what signs were you giving off - if any)?