Have you ever been in a relationship with someone that decided they wanted to be with the same sex instead?

This happened to me with my one ex , that I found out cheated on me with another girl and left me for this other girl , also a girl friend of mine , her husband left her for another guy. I understand there is bisexual people and understand there are gays out there but how is it that it took them so long to decide what they truly wanted? I was devastated when I found out my girlfriend was hiding the fact that she was Bi , if she was upfront about it , I would of probably accepted it but in this situation I didn’t have a choice , just like my friend didn’t have a choice when her husband decided he wants to be with a guy instead. Anyone ever experience this?
Have you ever been in a relationship with someone that decided they wanted to be with the same sex instead?
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