Welcome. I know this is probably the last place you'd like to be, but there are a bunch of kind, helpful people here, and we're all struggling with similar problems.
I've ML to my H once in the past 7 yrs, and yes, I know how seductive the idea of an affair is. I came close to starting an EA with an old college friend a while back, I'm pretty sure if we were on the same continent it would have easily turned into a PA.
What stopped me? I cared about that person, and myself, and realized that at some point, I'd have to make a choice, and someone (or more) would get hurt. When I stopped and looked forward....I realized it was not worth the fleeting feelings of pleasure.
Do you have friends, hobbies to keep you busy? How old is your S, is there 'guy stuff' you two can do together? I know it's not the same, but it can help a little to keep you mind off the empty place.
When did one of you move out of the bedroom? Why?
My H is also very quiet, won't discuss this sitch. with me, I have to sort of pick up whatever pieces I can get from the crumbs he throws. I moved to Finland 17 yrs ago, first to study, but I stayed because of H. So I have some understanding of the hurt you feel at 'giving everything' up for the R, and not getting anything in return.
There are others here who can probably give you better advice, I'm kinda thick in the middle of my own sitch right now, but you should probably give us some more details. Has your W ever said why she doesn't want sex? How 'involved' are you, were you when your S was a baby? Was there a point in your R that things were better, or has sex been an 'issue' since the beginning?