I'm going to sleep with a roommate's ex after my own breakup
Why would you sleep with a roommate's ex?
I need comfort and I want to feel different.
Needing comfort is understandable but you shouldn't seek it from your roommates ex. It will lead to problems with  your roommate and it could lead to one of you moving out.
Fuck you, my friends will be happy for me. I'm doing it either way.
I really think you should reconsider, there are plenty of girls out there you can sleep with that wouldn't cause problems.