My first partner didn't realise she was bi until well into our relationship when she realised she was becoming attracted to my best (female) friend. Since we were polyamorous anyway she was very open about it and it seemed like something she needed to explore so she did with my full support. It was a very beautiful relationship and I was so happy that she was able to find that part of herself and she ended up having other lesbian relationships. I don't see why a person who is in a married relationship should not also be able to explore other sides of their sexualities but to me this is why I have always felt monogamy can be too confining.