I think we need more details about the interaction with the son's girlfriend. It feels like there is more here that may have been glossed over that would inform a better response? Not being snarky -genuinely asking.

agree with PP - OP is not a reliable narrator. OP clearly is uncomfortable with any "alcohol related loosening up". What she describes just doesn't seem that problematic, other than OP saying she was bothered by it.

Also, if this is the only time this has ever happened, there's clearly not an ongoing problem. People suggesting al anon are bonkerballs.

OP, others in his life will be embarrassed for him. This is not all on your shoulders. You do not have to be the police.

You are not a reliable story-teller if you drink so little. You just aren't someone who can gauge the seriousness of his behavior. I'm going to trust in others to know better than you. And hopefully, they will make their objections known to him.

OP, you might want to check out an Al Anon meeting. They have them on Zoom.

Your husband is responsible for his behavior. He chooses to socialize with this guy, the guy is not responsible for your husband. Talk is cheap, what is his actual concrete plan for this not to happen again?

I don't think it's okay to ever use the silent treatment. It's okay to say you need o table discussing a particular issue for a bit so you can say what you want to say and avoid causing additional issues, but tabling a discussion doesn't include not speaking to your spouse at all for a few days or week.