Hi, girly1234, I'm so sorry you found yourself here but at least you're here now ... and not 25 years from now.
I'm also trying to figure out how this incident came to light, and whether he has been honest from day one about his claim of bisexuality. For many of us, including me, our husbands find it easier to claim to be bisexual rather than to face the fact that they're gay. And, at least in my case, sexuality changes with time. A man who's able to have hetero sex when he's younger, finds it harder and harder to perform as he ages. My husband's sex drive was weak when we were in our 20's, and got weaker and weaker with time. The only reason I never suspected him of cheating was because I figured he was impotent. So I was really shocked when I learned how active he was ... just not with me. I went for over two decades without being touched, and when I finally confronted him, he said "I have always known that I was bisexual." As if our vows of fidelity only applied to hetero partners, but same-sex partners were exempt.