One thing you will read over and over again is, when the existing relationship is in trouble, that is not the time to explore poly relationships. Fix what's broken, then spend a few years discussing opening the marriage if she still feels it's necessary.
Communication is key for any relationship. I would guess that she may have tried to hint that the neglect was getting unbearable but you didn't catch on. This is where the counselor will come in and help each of you figure out how to speak each others language and have the other fully understand, instead of expecting them to "take a hint" or "read body language", etc.
PS. Speak with your doctor about the low libido and other ways to manage your stress levels.