Dress it up however you like; we're talking being unfaithful.
No we aren’t. This kind of biphobic nonsense is really stigmatising and unhelpful. OP is NOT talking about cheating, and it is an absurd stretch to suggest that she is just because she has realised something fundamental about her identity late in life.
OP - please just be aware that I have, many times, witnessed really shocking levels of biphobia on mumsnet. There are many posters who will refuse to accept that being bisexual doesn’t make you more likely to cheat, less able to stay in a committed relationship, etc. Please don’t take comments like that to heart, because they are only reflective of the ignorance of the people who make them and not of you.
My perspective on your situation is that I understand completely. I am bisexual, married to a man, and not ‘out’ to most people. My husband knows and is absolutely fine with it, but my family don’t and lots of close friends don’t. Although I have had a couple of relationships with women in the past, they were never serious enough for me to take the step of telling my family.
It does feel to me like quite a large part of my identity is unacknowledged and unexplored. I am so in love with my husband and so happy with him, but it’s not very easy knowing that I’m bi and it being a secret that has never really been openly expressed. I completely get why you feel like in coming to this realisation later in your life makes you feel like you’ve never given an important part of yourself any kind of free expression.
It may help you to remember you’re not any less valid, or any less bisexual, for being married to a man and having realised late in life. The relentless grind of heteronormativity means that it is very, very common for bisexual women not to recognise that they are bisexual until later in life. It doesn’t make you any less who you are.