This spring I defended my PhD. The very next day I had to fly home to see my cousin, who I grew up with, one last time. She had cancer and died about 5 days later. I am very sad that she is gone, but extremely happy that the timing of events in my life happened such that I was able to get home one last time to see and talk with her before she passed. So, hopefully you will get an explanation for cause of death, but either way maybe you can try and remember a pleasant event with your roommate and use that as a source of comfort. We can't always explain events in life, but we definitely have the power to remember and enjoy what has happened.