Lesbian Relationship Challenges Support Group
This community is for those who are in a gay marriage, and the unique challenges that may be had in a same-sex relationship. Find support and talk to others in a same-sex marriage, and get advice from the experiences of other members.
Your girlfriend needs to be honest about what is going on. If she is planning to transition, she should probably be speaking with a counselor. And it might not hurt for you to get individual counseling or couples counseling, in order to determine if your relationship can survive a transition of this magnitude.
Testosterone is going to bring big changes. This does not necessarily mean your partner will develop a bad temper, but your partner is definitely going to look and sound like a man.
First, you both need to have an honest discussion about what's going on.
I wish you both the best.