So when it comes discussing threesomes

Why is it okay for a man in a relationship to have a threesome with two women but when a woman ask can she bring another guy it’s look at different?

Like I can’t have my cake and eat it too? I told my boyfriend we can have a threesome but when I brought up with a female he was cool but then I was like with another man he didn’t like it ? How can I convince him to like it ?