Boyfriend being secretive. What do I do?

My boyfriend has recently made new friends. Doesn’t say much about them. Never tells me when they all hang out, sometimes even lies about it or pulls a “oh I thought I told you” once I find out on my own. Recently found out his friends are women. And he was extremely careful not to ever mention it by saying shit like “someone” or using gender neutral terms until he slipped once. I don’t care for him having female friends. But for these to be fairly new friends and for him to be so secretive about them makes me very upset. And I know sometimes they hide it for the reaction. But for me, there would be no problem if he had just been honest and open rather than trying to hide the facts. What do I do?