Zig you're my girl but I gotta say you are all over the place about this weekend. A few days ago you were talking about how upsetting it was for you and now you're talking about possibly throwing a party. So one thing comes to mind......
Be Still.
Don't over think this whole thing. You don't know if he's even stopping by and you're thinking of what you should do in order to affect an outcome.
It's not your job to reassure him that you're "okay" with him going to spend 8 days away from his son with his GF.
No pats on the bum, no have a good time. A hug, a warm goodby, and a see you in a week is fine.
Starsky is right let him wonder about you.
I know I advised you to find a way to be happy that he was having a break from the house or whatever but that was to combat any bitterness you might be feeling that would play into your interaction with him. There is a thing as going too far the other way and actually supporting him emotionally in having another relationship.
Keep yourself on solid footing that's the only outcome you need to try to influence dear girl.
