Rob, just want to add my welcome to you.
There are quite a few people who are poly in their hearts but who choose to live a Monogamous lifestyle, often because they feel committed to the promises they made their partner. I applaud folks that do that - sticking to promises made is a sign of commitment, in my mind.
Renegotiating your relationship is something that many have done in the poly world - for many reasons they entered into a monogamous agreement and realised that it just wasn't them. This is often associated with feelings of guilt (for making promises that they realise they can't keep and be truly happy). It is often a shock to the other person when faced with this reality - paradigms need to be shifted in order to continue to make things work - change is not something that is easy to embrace when it is something as fundamental as a life-long relationship.
I wish you luck on the path you choose.
Please check out The Birdcage - an open, friendly Polyamory forum for all parts of New York State
"Listen, or your tongue will make you deaf." - Native American Proverb