My 2 cents worth. I think it mainly when i started going through major depression - I have always dated men and not given another woman a second look. Suddenly I really connected with another woman at my work. She was divorced and I was in a relationship with my Boyfriend. We had both never been with another woman. Yet we started an affair due to the intense feelings between us and how we could relate.
I eventually broke up with my bf, and thereafter my relationship with this other woman also ended.

Right now I am back with my same old boyfriend.

I have never otherwise been attracted to a woman and am not even sure if I would label myself as bisexual.
It is confusing and when battling with depression and similar, all you want is someone to understand and support you.