Call it a whim, perhaps even a passing infatuation, or maybe it is just because it has been so long since I have gotten any physical attention from my wife but, I think I love you! You have my undying respect!
However, your post makes me shudder. So much of what you say rings true for me that I fear my marriage will fail as well. Like you I have been the patient, supportive, and nurturing husband. It is a double edged sword to be sure. You cannot tell them you are miserable because that puts too much pressure on them, and you can't act as if everything is ok because they will think it is and nothing will ever change. So you are left "holding the bag" but this bag is not empty. It is chock full of frustration, hurt, sadness, and fear. Just remember dude, when you leave, give the bag to her, after all, everything that is in the bag exists because she was not willing to pull her weight. Forgive her, forgive yourself, and start over (just don't get married right away, go have lots and lots of meaningless sex for a while, just make sure you wear a raincoat).
Boy oh boy, don't they just love to bash that "depression" thing over your head. I mean, what can you say to that?!?! If if you do anything but completely ignore your NORMAL AND HEALTHY desires and say something like "It's ok honey, I love you and we'll get through this." you get crucified. YOU Mr. Normal and Healthy have NO VOICE! BAH!!!!!!!
One more thing, even though the LDrs like to say it is a challenge, obstacle, (insert newest "PC" term here), loss of sexual drive (for any reason) IS A HUGE PROBLEM, and there is something WRONG.
Sorry, went off on a rant there. I hope my marriage can make it but I really respect you and your strength for what you are doing. I feel like you are taking a stand for me and others in our situation, others who are painted out to be the bad guys because of our normal and healthy drives. Bravo I say, BRAVO!