I definitely would not advise calling the police just to report his drug use at the party.
But i definitely would take steps to protect yourself legally with him having that car that has your name on it with drugs in it (even if it is just on his person) and with him not having a valid driver's license.
I would definitely advise you to set boundaries on that issue. I cannot say for sure what choices there are in regards to that. I will say that when my son was 18 and out in "his" car, i had the title put in his name and my name taken off it. I know that's a tad different that a married couple, but maybe it's not that far off.
So i guess what i'm saying here is your boundary-setting has to do with your protection (legal, emotional, physical, etc).