I'm sorry to hear of your dilemma.
You are almost certainly correct that your husband is both jealous and attempting to pass strict moral judgment--and perhaps for a good reason.
First of all, given that the two of you have failed to agree on a JPA, the judge ultimately will determine all the issues relating to the agreement. Issues that each of you have agreed upon will likely be signed off on. The parenting agreement, at least as it concerns sexual relations, or the appearance of sexual relations, between either of you and a third party in your respective homes while the children are present, will be solely determined by the judge based on the best interests of the children.
There have been a number of psychological studies in which it was found that the psychological burden that children bare is increased with the introduction of a new romantic interest of their parent's. Many attorneys issue sage advice to their clients to specifically avoid that which you are fighting to preserve the right to do.
Here is a link to a site of an Illinois attorney who has gone to great lengths to provide insightful, and often court-followed philosophy regarding parental behavior in divorce and custody cases:
While it is impossible to predict what your judge will rule in this situation, you risk losing much if you are unable to compromise now.
While you have no doubt considered these options, I will put them out anyway:
1. You might agree to have the no sleepover rule only apply on nights that you have custody of the children.
2. Write in a provision that the limitation ceases automatically upon your engagement.
3. Get married. Even the court can not prevent you from residing with your spouse.
I wish you and your children the best.