I'm quite new to all this as well.
Your situation sounds familiar to me (aside from it being F-M-F in your case and M-F-M in mine).
I do anticipate that someday my wife and I will make plans for her to spend a weekend (or longer) with her new love. It already pains me in anticipation, and I am always upfront and honest when we discuss this. But I also know how important it is for them so it becomes (by proxy) important to me.
As has been said already though, it would be best to set expectations prior to parting ways. Then if he doesn't call you, you have every right to hold his feet to the fire, lol.
I also know with my wife and her love that when they are together their new relationship energy is very strong, and it is very easy to get jealous towards that. Alot of people here know what you are going through, you're in good company.
Best of luck!