[Jaguar]

Well, it's probably not just a passing phase then. The best thing to do is find a quiet time and tell there's something you've been meaning to talk to her about. She probably already has some idea since she lives with you and knows you. She notices if you date girls or not and what your interests are so I don't think it's going to come as that big a surprise to her.

Her reaction is going to be difficult to predict. Mothers are usually more in control in situations like that than fathers are. Unless she's extremely religious conservative she's goint to tell you that she's still going to love you and you're still her son. She will know it's going to be a difficult time for you and hopefully she'll offer some support. That being said, try to be understanding of her. Her son has just confirmed her suspicions that he's transgender and will never do the wife-and-family-two cars-surburban house thing. She has to deal with that and it can be difficult for her to do.