my guy is interested in trying...

So my bf wants to have a threesome, but I'm really hesitant to the idea..especially since he wants it to be with one of my friends.. I want to make him happy, but I wouldn't want to do it with anyone that I personally know. Does that make sense? Or am I just being weird about the whole thing?? He also hasn't brought it up in a while since he knows I'm not 100% ok with the idea. Help?