I have only read your original post so not sure what went wrong in your other thread.
I have a few bi friends who are married (both same sex and opposite sex) and I do find it odd when they get upset if someone describes them as straight or lesbian (depending on sex of partner) and they have to correct them.
I can't see why sexual orientation matters once you're in a committed relationship. He's bi, good for him. That doesn't mean he can go and experience men so why does it matter?
Has he said why he feels the need to share this? Does he need to feel 'special'?
Why are you upset? Do you expect him to cheat?
All a bit bizarre, I'm sorry he's thrown this at you and I'm surprised your dd didn't just roll their eyes.