My boyfriend is truamatised what can i do?

my boyfriend and i have been together for almost 7 years old now. He is 4 years older to me and we both are quite young..im 19 and hes 23.

very recently my boyfriend and his 3 friends were going out ..they travelled in 2's and one of the vehicles had a major accident. The 2 friends in it were rushed to the hospital by my boyfriend and the 3rd friends...after a couple of hours in the ICU they pronounced one of them dead and the other unresponsive.

My boyfriend spent all day with them and had to see his friend die brutally in front of his eyes. He is really traumatised and fears even stepping out of the house anymore. He thinks about death and their families and is constantly fearful. He is also afraid that the families may take severe action and he may get struck although he wasnt driving nor was it his vehicle...it isnt his fault in anyway but he feels like everyone thinks hes the culprit.

im not going to ask if its normal because i know it is and i know how awful it was. i just want advice on what i can do to help him get over such a scary phase.