How do you feel when your boyfriend goes out to drink?

When your boyfriend goes out with his friends, guys night, whatever? Can anyone help me get over this ANXIETY I feel? 
My boyfriend and I are both 20 and in college. We've been together for 2 years and we're both in love and loyal, I know he wouldn't cheat. 
Today he was playing basketball at the park w/ these guys he barely knows (met them like 3 times there) But they invited him out to get food. Next thing I know he's drinking at the bar. Just a beer & soju he said (soju isn't hard liquor is it?? He claims it's not as strong as vodka.).
Anyways. My reaction when he goes out with his friends (or people he just met, like this!) is always I don't like it. I'm worried. I don't know why I'm worried. I don't think I can relax until he calls me when he gets home, which he said he was going to do. I guess I worry for his safety? I'm afraid he might drink too much? Shit happens when you drink too much...
I'm not sure how to just, be cool, you know? NOTE: It's not terrible anxiety. It's just a constant worry I would love to get rid of. I don't know why I worry. I have a hard time turning it off. 
Anyone else here worry like this for their SO?

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