Personally, I felt I owed it to my fiance to tell her before we get married, but I absolutely understand those who just can't make the reveal. I still feel a sense of dread when I think about anyone else finding out. I knew she wouldn't be happy about it, but I was 99% sure she would accept me no matter what, as she had already stuck with me through worse. It was three years into the relationship, and I had been doing things to try and soften the blow, like "joking" about trying things on when I'd go shopping with her (something that stopped after the reveal, unfortunatley), talking about being curious how it felt to be female, and taking one opportunity to correct her belief about crossdressing meaning you're gay.