As usual, I agree with Cheyanne. Strangely, I agree with PF.

I don't even want to think about how the threesome would be possible under the conditions you'd be comfortable with and I don't mean that in a critical way.

I've come back to this thread twice and, if I may read between the lines, see that you want to please him yet don't want to do a threesome.

Why don't you both just watch some porn while you're having sex or even talk about another woman while you're having sex. (Sample convo example: What would she be doing to you right now? She'd be ___ on my ____, etc.)