Him and another lady did what they could to help your kitty, but his/her injuries were too severe. Boyfriend says he doesn't believe the cat suffered long, and feels terribly that he couldn't do more. He made sure to move kitty off the road.
Of course the arsehole driver of the car who hit the cat didn't stick around to take responsibility for their actions...shame on them! :(
I hope this reaches the owner, so they can stop wondering what happened to their cat. —Sorry for your loss :(