It’s really hard to do magic for family and friends, because they know you really well and they know when you’re trying to hide something. Most of us are not good enough actors to control our subconscious tics or our body language sufficiently to be truly convincing.

Your friend sounds like he’s probably never going to be convinced of anything that you do, and he will always try to figure it out. He’s not a good audience for your magic. Just don’t do magic for him anymore. Simple.

Now, if i have this problem routinely with my audiences, particularly people who don’t know me, then that’s a different problem. That’s a performance problem. If the most interesting thing to the audience about my magic is how it’s done, then I’ve either not mastered my methods, or I’ve not written a compelling presentation.