Is it okay to have boundaries around partners' behavior at my workplace?

Is it mean for me to have the same standards for all of my partners when they visit me at work? I'm a private person in general and I don't don't act coupley with any of them when they come in. My boyfriend is more openly affectionate than I am and he was upset about me not receiving his flirting well. I tried to explain that I'm reserved with all of my partners, and that my job/professionalism are important to me, but he just got more upset and now he keeps saying he won't discuss it with me.

That is absolutely not “mean.” It’s completely reasonable to have boundaries around PDA or other behaviors at work. I think people visiting their partners at work should absolutely respect their partners’ wishes about how to behave. You don’t need to agree, or understand, or like it. Everyone’s work culture is different and everyone’s preferences around how they’re perceived at work are different. That’s not really something up for discussion or compromise.

Your boyfriend is being unreasonable on two levels: one, whining about his preferences not taking priority while at your job, and two, refusing to talk about it with you now. That’s not a mature way to deal with conflict or emotions. You are not being mean, he is being petulant and selfish. Don’t give in to this tantrum and concede that he should be able to trample your boundaries around work, don’t wheedle and cajole to try and get him to talk to you, don’t validate his perspective by getting drawn into an argument about having to prove or convince him that he should behave the way you need him to behave at your workplace.