As I see it, an open relationship is where a couple mutually agree to remain true to each other in mind, but not in body.
The integrity of the relationship, together with any future hopes and ambitions the couple share, need not be adversely affected by their individual sexual dalliances with other parties providing both are coming from a place of emotional security and can trust the other not to exceed any agreed boundaries.
Questions to be resolved prior to embracing a change to the accepted norm include, but are by no means limited to, whether all such liaisons should be of the one night stand variety, are mutual friends fair game. should there be a moratarium on forming sexual relationships within the immediate neighbourhood, what happens if extra marital/curricular activities result in pgs, etc., etc.
Problems with this seemingly Utopian existence can manifest if, for example, one party becomes infatuated with a third party, spending all their available time with them and being emotionally/physically unavailabe to their alleged life partner, who has paled into insignificance in comparison with the more recent paragon.
Difficulties can also arise if one party is more successful than the other in forming sexual liaisons, leaving the other party to twiddle their thumbs while their beloved if off out shagging with their latest squeeze(s).
On a mundane note, consideration should also be given to the hit the family budget may incur should funds be diverted to provide entertainment/gifts etc for assorted paramours of a transient or more permanent nature.
From what you've said, what you have is a far from open relationship in the accepted sense of the term. Had he previously determined that monogamy was not for him at the time of your marriage, your h has committed a gross deceit in not making you aware that he had no intention of keeping the vows he made to you - and/or to any greater being if the ceremony was religious in nature.
As it is, he's waited 15 years and has committed further deceit(s) before informing you of his liberated view of sexual relationships.
The resurgence of passionate sex, meaningful conversations, and revitalised intimacy are not uncommon in the 'hysterical emotional bonding' that can ensue after the discovery that, unknown to the deceived party, a beloved has been having it off with ow/om turned their sexual attention elsewhere.
It may be the case that you'll discover this 'high' is as illusory, or more properly, delusory, as the probable bullshit your h is telling you in order to have his cake and eat it and, in common with many others who have been wronged by deceitful and conniving spouses/partners, this 'second honeymoon' period will be shortlived as you begin to realise that, at most, it represents a holow victory, a temporary triumph of hope over experience.
By adopting your h's alleged philosophy you may find you are able to resolve any issues you may have around 'unwanted jealousy' once you have experienced the sexual attentions of other men. Or it may be that any such liaisons will leave you feeling less than you can be.
Before setting foot on any path that is alien to, or at variance with, your personal social mores and beliefs you are best advised to carefully consider whether it is likely to enhance your life or destabilise it.
The fact you feel unable to discuss your new 'open relationship' with any of your close friends suggests that you are not entirely convinced by your h's reasoning. Do you fear that if you broach this subject, you'll meet with a 'shock horror' response or be laughed out of court?