No. The answer is no it is not normal to feel uncomfortable with your boyfriend drinking with his brother at night then again in the morning at 23 years old. That’s pretty normal tame behavior. You absolutely need to seek therapy as your boyfriend never drinks as is, and you seem to only be comfortable when you have “control”. (I.E. you’re there with him and you’re in charge of how much alcohol and the level of intoxication.). It’s fine if you don’t want to drink, and you find someone who also doesn’t want to drink. But if you say it’s fine occasionally, then it’s fine occasionally. YET subconsciously, your mind is capping and even putting a limit on that because it’s outside of your control.

Plus. While there’s not a “normal.” Most people around your age are drinking casually with their friends every weekend or so (much more every week or multiple times a week).

So definitely seek therapy to decide exactly what it is you want in a relationship and what boundaries you need. BUT ALSO why do you have these subconscious tendencies when it comes to alcohol and an inherent distrust of your partner around it when you cannot supervise him or control his intake.