Rosie,
I normally don't post much anymore but your story is troubling..
I just wanted to throw a couple view points out there from a straight male and as someone who was discarded decades later;
As a straight male I would never act like or pretend that being attracted to men is some normal or casual thing I could do. Straight guys just don't do that and talk that way about it. We would never say we were bi and changed our mind..
It could be a stressful marriage for you..is he meeting a buddy for a beer or is it a date? If he's on travel with some guys is he having sex? Why should you have to wonder.. The stress can eat you up.
My strong fierce love for my now ex could not fix her or keep her faithful..even after decades of friendship and life together. She was willing to throw everything away..the entire life we built, wedding vows, our home..all to be with a women she knew only a short time.
His honesty is admirable and his love of you now may be strong. But you have seen yourself..there are no take backs when someone has a same sex attraction..you can't unsay it..
Sincere wishes of strength and wisdom..