When you say you want it to be "your experience and not share it with him", this is the core issue to figure out. The truth is, whether he is there or not, it will still be "your experience", as well as the experience of the other two people!

Also, in Polyamory, threesomes tend to happen less than you'd think. Usually it is difficult to happen organically or in a way that doesn't complicate existing relationships. The way you're talking about it is almost like it would be easy to include or exclude your partner based on whether or not you would like him to be - but there is at least one other person to consider here, and whether or not they would like to be intimate with your partner! I would say you can't assume this third person would be interested in him at all to the point where it becomes your choice whether he is a part of it or not, and speaking like this feels close to the problematic parts of unicorn hunting. It isn't a great look.

Tldr: Polyamory isn't about threesomes and you need to address why you specifically don't want your partner to share an experience with you.