If there are risks for getting pregnant when on Lexapro, she is probably worried about a
lawsuit, but frankly she has no business making your boyfriend sign anything. Maybe she just doesn't want to have patients who are on Lexapro.
If you are angry about this, you could talk to a lawyer that specializes in malpractice. Your doctor really crossed the line, I think, and perhaps a letter from your lawyer would stop her from doing this to other people.