One of the books out couples counselor has asked us to read is called Passionate Marriage. The author means the book to be for any couple whether legally married or coupled or whatever their case may be and for individuals. This book is about a concept called Differentiation, which is basically what you are showing here Mono. Differentiation is the balancing of individuality and emotional connection or togetherness. People who are able to differentiate are able to change or adjust either side of that equation without "going off the deep end".
You say that you are able to change parts of the togetherness of your relationship to keep the individuality you have and you have already shown how you have changed your individuality to keep the togetherness by being the Mono in a poly relationship.
I commend you for your success so far in this difficult task and wish you luck with it for the future.
Life is about the journey and not the destination,
so what better way to know life
than to wander all the roads and paths set before you.