i think you have a right to be concerned but try not to worry about it too much, as silly as that might sound right now. you worrying about it isn't going to make it better, it only ties your stomach in knots.
if you knew the general area of where he was, you could anonymously call 911 and report suspicious drunk driving.. that way you wouldn't risk the chance of him hurting himself or someone else on the road.
and don't be nervous about posting here - we've all been in your shoes!
