Hi there,
Sorry to hear that you are in this position and understand how it can feel being in such a position. Sounds like you have decided who you would rather live with, so finding someone else to take over the one you paid a deposit for, would be a good start. I know it's probably easier not to find someone and stay in the one you have booked, but living with the right people makes such an impact on your life and studies. It won't be a nice feeling but firstly, I'd speak to your mates who you no longer want to live with and if they are true friends will understand and help you find someone to take over. The best way to be in this situation, is to be honest and just let your friends know your decision. Who knows they might know of someone who is looking for a place. Facebook and FB groups are a great way to find someone to take over a tenancy.
Hope this helps and you make the right decision for yourself 🙂
^Zac