Advice for being there for someone during loss

Lastnight i had to give my roommates boyfriend CPR because he stopped breathing (he overdosed & we have no idea what he overdosed on we just know that he's had a really bad drug problem in the past) the paramedics came and they worked on him for about 40 minutes and they couldnt get his heart to start beating.. I wish i could have done more & I have no idea what to say or what to do to help my roommate. My roommate whose like a sister to me has bad anxiety and depression as it is and I feel so helpless because i couldnt help him & i don't want to lose her or watch her lose herself so if anyone has any advice please give it to me & I appreciate it so much.