Is it normal to feel guilty about something even after people tell you it isn't your fault?

Driving home last night, I swerved to avoid hitting a deer.
The man driving behind me must have not seen it, or swerved late because he hit it head on.
He then swerved out of the lane and into a tree.
He was unresponsive when both myself and the other driver who stopped went to make sure he was okay [AFTER calling 911].
The ambulance arrived a while later and after they got our statements and phone numbers, they told us that he had died and that he had most likely died on impact of hitting the tree.
I went home and after being calmed down and told it wasn’t my fault by my boyfriend, I still couldn’t sleep.

My mind keeps telling me that I could have done something differently and prevented him from dying.
There were two empty car seats in the back of the car.. this man had KIDS.

Is this normal to feel this guilty?
Is there a way to deal with it?