Eric was a priest so I am sure that his conscience is very sensitive. Daniel was a very good friend to him which also increases his guilt. Nicole was his first love which multiplies his guilt.
As bad as DUI is, I feel it could be different if Eric killed a stranger, however he will always be tied to everyone involved in this story. As for Nicole, she of all people should know "there but for the grace of God" with all the nights she was drunk. Much loike Brady who told Eric it could have been Brady during his drinking days.
Lets face it, Eric has been through he!! this last year – Kristen’s seducement, Nicole’s betrayal, Sarina ‘s agenda all those could send anyone over the edge!!