Do you have a strong trans support network? I wonder if you may be best served by gaining the advice of folx who’ve been in similar situations.
If you don’t have access to a good one, I have a great one! Please feel free to DM me and I’ll connect you with them.
Have you talked to her about her feelings about trans people?
Before you go farther, you really need to level with her. Some people are into hairy guys no matter what is going on below. Other’s are turned on by specific genetalia. And some just get swept away by personalities and wanting to mash up against the rest just follows. You really can’t tell which this woman’s preference is unless she tells you.
So I think this should have definitely been mentioned before fooling around, particularly if the other person is as good a friend as they seem to be.
I’m reasonably flexible in my preferences but I’m not sure I can give informed consent without knowing the big impact sexual details (orientation, sex, gender, and if this is a first something) of the person involved – because that information is used to inform my own sexual desire and also avoid possible social landminds.
That being said that ship has sailed so now you’ll need to tell her. It’s possible she might have guessed but also unlikely from your post.
If it were me I’d do it somewhere that gives both of you a safe exit (you don’t know how she will react). unless it’s dishonest I’d lead with something like this, “so I really enjoyed the other night but it occurred to me I’ve never actually explicitly had
discussion with you about my gender/sex identity. I’m FtM and I am out but wanted to make sure you were aware and ok with it before this went any further…”
Then let her lead the conversation, give her space and don’t be surprised if it’s a deal-breaker.
I would go with something like “hey there’s something important about me that I haven’t shared with you yet and I thought it was about time to let you know. I don’t talk about it a lot so that’s why it’s never come up before.” Just kinda level with her and be honest but don’t make a big deal of why you haven’t told her before or even why specifically you are telling her now. You were never obligated to tell her. If she asks if this has something to do with you making out then yeah tell her you wanted to make sure she knew in case it changed her mind. But I don’t think you need to spell that out if she doesn’t ask.
Can’t offer to much advice but I do want to say if I were in this situation I wouldn’t care once you told me! I would be happy that you told me and definitely really shocked but I wouldn’t let it change what we had going on. I’m a 25 year old female who has only dated guys but view my own sexual orientation differently than society. I like a person for who they are on the inside not on the outside so you being trans wouldn’t be a problem. I know however that not everyone is like this though. Sorry I didn’t help much but hopefully gave you a little reassurance!