Thank you for taking the time to respond, even though you didn't think it would be much help. I inevitably stood my ground, and I told him I wanted him to be happy, but he had to give me more time, and not spring her appearance on me, because I feel as though that should be warranted. He still didn't listen to that and brought her to my graduation ceremony without my knowledge. :/
I suppose we will see where this goes.

My brother has had difficulties in the past with self harm, depression and anxiety, which is why I'm assuming my father jumped to the psychiatrist. (I probably wasn't clear, but he's the one who wants me to go.) I never really got depressed or upset after the divorce happened, my brother took it terribly though. I think he just assumes something isn't right in my head, and those are the folks we are most familiar with through the experiences my brother had. He (my father) told me he doesn't understand why I wouldn't want to be around his girlfriend, or why I prefer to be alone rather than go out, etc, which is why he wants me to go. It's weird. I figured I might as well go and just have them prove to him I'm okay.