Can female/male coworkers have an innocent drink?

My boyfriend who is 37 works as a teacher. Can he have a drink once every two months or so with a female coworker without it being anything suspicious? They went once in June for an hour and I knew where he was (around the corner of his townhome), who he was with, and I was at his place watching TV. He brought her in to introduce me to her. Now that school has started again, I am worried that he will be doing this regularly. Not that he has indicating this, but he told me that having a drink with her or with any coworker after work once in a while, with my full knowledge of where he is, who he is with, and how long he will be gone is not anything to worry about. Am I being excessively jealous here? I went as far as to tell him that if a man and woman (regardless if they work together) are having a drink alone, it is a date. He told me I was crazy because a date means there is romantic intent and not an innocent after work drink once every blue moon. Am I being crazy?
Can female/male coworkers have an innocent drink?
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