How can I respectfully tell my friends boyfriend that I want to talk to my friend not him.

So my friends boyfriend apparently has access to their phone which is fine but he keeps on responding to my messages. He’ll use a special font to distinguish that it’s him. I was fine with it the first few times but now I just want to talk to my friend and not him. I’ve never met the dude, he’s nice but if I wanted to talk to him I’d get his number. But since my friends really likes him I don’t wanna be mean. How can I respectfully tell him to stop replying to my messages and just let me talk to my friend