Unless I was just hooking up, I probably wouldn't keep my transness a secret. It's a huge part of my life, and in addition to honesty being a good policy in relationships, I don't even want to keep it a secret. Sure, being trans is kind of horrible in all kinds of ways, but you know what, I've transitioned, and it was really hard, but now I kind of want to hold on to that like a trophy, like "this is my determination, this is how important it is to me that I identify as female" and if my partner isn't willing to accept me after I've shown such strength, it never would have worked out anyway. They just have too many hangups. If they have problems with your physical body, like if you're pre-op, and they made some false assumptions about what sex would be like, it really can't be helped much, and you just have to hope for someone down the line who will find you attractive and love you regardless.