This is an interesting thread. Biking for over 45 yrs and have been hit 5 times. I've had acquaintances die by car, a competitor in a road race I was competing die in a head-on collision with a truck, a friend get hit and 15 yrs on, still needing round the clock nursing care. Been hit on a tandem with a girlfriend, commuting, and during training. The last time was 5 yrs ago when sideswiped by a woman in an SUV who couldn't judge overtaking me. She never stopped. Luckily, it was 30 yds. from my home and my neighbor dragged me out of the road, before someone else could hit me. It resulted in a torn up knee, lots of road rash, a broken arm , bruise to the jaw and a concussion. I write this because after healing, I went through a time with thoughts similar to the OP. It was hard to get on the roads again with out that dreaded anxiety response.
So how did I get over it. Using a mirror, flashing tail light, never riding at night or in the rain, planning routes with the maximum number of bike lanes, incorporating off-road riding and Zwift (indoor training) into my workouts. I will pick up a Varia Radar as a poster above suggested and lastly, just riding defensively and communicating your intentions. Most car drivers don't WANT to hit you (yeah a few do), but letting everyone know what you are going to do allows everyone to react appropriately. Good luck and hope you get out there.