Photoguy, I find your confessions about why you might stray from your marriage quite in contrast to my thinking. I believe that most of us men on this board would stray because we are NOT haveing sex with our spouse. Indeed, your situation is precisely why your W could possibly stray. Instead, she is leaving.
Also in contrast, I have sexual fantasies about my W. Is this normal? Perhaps it is the wanting what we do not have? Same reason you only fantasize about other women. I too look at other women but want to take those feelings of arousal to bed with W rather than act on them with another woman. Nonetheless, my greatests arousal revolves around my W.
All this makes your sitch that much more of a quandry. You are a HD man with your fantasies, a LD man with your W. You want, but only from those from whom you cannot get.