Speaking as someone who's closer to your dads age than yours......First thing that comes to mind is how old is your girlfriend?Isn't there a legal age when you can become transgendered?If your having sex?....I think i'd be more upset about that.....15 is way too young to be messing around. And throwing in the bisexuality just makes me think your confused.
As for your dads reaction...It'll probably depend somewhat on the answers to those questions.

If he's prejudiced and quick tempered....The best suggestion I can give is ......Slow assimilation......Have the "friend" around more often....If she's coming over say once/wk make it 2x/wk or more.....It'll give your dad time to adjust and grow to like this person for who they really are. Telling him everything at once will not give you the reaction you want. :)

to answer the question about being too young to be trans-gendered is kind of impossible to control. It is a birth defect. (not in as much as we feel it is a defect that anyone can see but still a defect none the less.

As far as you advice about this childs sexuality, excellent advice for sure. At 15 years old, you really need to take your time when deciding what your sexuality is going to be. There is too much time available to be hurrying this topic.

Good luck,
brian

"to answer the question about being too young to be trans-gendered is kind of impossible to control. It is a birth defect. (not in as much as we feel it is a defect that anyone can see but still a defect none the less"

thanks brian, I assumed transgendered had something to do with chemical or surgical changes....Never occurred to me it was something you could be born with :oops: ......Learn something everyday. :)