It sounds to me like its time for you to step up and take ownership of your own choices again and their consequences.
So, have you asked yourself if you want SO to stay over on Saturday? I am NOT saying whether you should or shouldn't. What I am saying is that you should do what you want. This isn't simply his choice.
What do you hope to get out of it? What are the possible positive and negative consequences for you? How do you feel about SO supposedly deciding that he would spend the night? (I say supposedly because it is equally your decision.)
I sense that you are feeling used. Will this be something that will make you feel used? If so, why would you choose it?
Under what circumstances is it OK with you for SO to stay over? Do you need to know that he wants to reconcile? Are you open to having no expectations and just seeing what happens?
BTW, I think in any case whatever you choose to do, it may help you to get a bit more emotional distance. You aren't really giving him any space to miss you or to pursue you.
Roughly, it sounds like you are always two steps ahead of him in kind of this way, if it makes any sense, lol.... you are opening the front door as he steps onto the doorstep before he gets a chance to knock....
This is also the reason you don't know if you are in denial or not. You are too afraid of not being the always-opened-armed-welcome-back-whenever-you-decide-you-want-me NM (because, gasp, he might leave -- of course, he already has left...), to give him space to show you that he really wants you back and will make an effort to get you back.
That is, you don't know if you are in denial because you aren't giving him space to make his intentions clearer.
Another weird example.... You are dishing up a second serving at dinner to him even as you ask him if he wants it without giving him a chance to respond. So, you can't tell as he nibbles at it if he is being polite or really enjoying second helpings.
