How do I tell him

So one of my guy friends wants to meet up with me and hang out and I have a boyfriend and mention my boyfriend all the time. So I was on FaceTime with sometime last week and I paused him and went back and he was in boxers.. Um no that’s rude.

So I told my friend how he wanted to hang out with me and immediately she said ‘don’t go, he’s going to make a move.’ and I don’t plan on putting myself in that situation so.. how do I tell him I can’t go without being rude.