I can totally related to your situation. I was married for 30 yrs to a man. I would get these intense crushes tho, like you describe. I always tried to hide it, but he always sensed it. It was pretty fucking horrible. I never cheated, but he always thought I did.
We did tons of marriage counseling.
We had 3 kids, had a lot of great stuff in common, but we grew apart. This poly/mono thing was def a factor. He and I tried poly together eventually but it didnt work for various reasons. (see my post in personal summaries)
I wish you luck! I know exactly how you feel about not wanting to give R up. *hugs* Mags