Instead of projecting what you think his feeling are.. how about YOURS? The more time spent talking about them, the less we give to ourselves. It's kind of like that pesky mosquito buzzing in your ear. That's all you can hear until you focus on something else. And it's great when that annoying whine is gone.
What's wrong with telling his best friend and co-parent that you need a little time and space to adjust.. and that him not sleeping in the house, on the couch would be very helpful to you.. that you need to get the feeling of what it's going to be like on your own. Ask for his help in that regard rather than making a demand.
Having sleep overs with friends is a beautiful thing!
