Using Facebook messages to get a civil injunction

My girlfriend has a new partner whom she cheated on me with, and when I found out about it I told her to take her things and go stay with him. Before she left she issued a death threat saying she would have her father come and kill me. Her partner came to the apartment after she left. I logged into her Facebook account without her knowing, and according to the messages I read he had a gun with him when he arrived. Also in the Facebook messages, they conspired for him to come into my online place of business (my Twitch channel during a livestream) where he harassed me and doxxed me by using my real name in chat in front of other viewers while I was live. I also learned from her message history that they have been stalking my Twitter account, my Twitch streams while I am live, and may have even joined the community Discord server for my Twitch community. Can I use this info in court despite not having permission to access her Facebook account?