"When enabled, sims will only get jealous if they are not romantically interested in both parties"
what mean "both parties"?
Sim A, B are lover / Sim C, D are lover / Sim E is solo
are they party sim A+B? and C+D?
when A and C kissing while this option enabled, A is romantic interested in A+B party, C is romantic interested in C+D party, So B and D nobody will be jealousy to A or B?
it seems Sim A has lover = Romantic interested in A+B Party, So nobody jealous to A whatever, because this option make jealousy work only "not romantic interested in both parties" but Sim A has romantic interested in A+B party?

If the feature were working as it was intended, it means that sims A, B, and C would all have to be romantically interested in each other. That's what Polyamory is, a multi-way relationship. It doesn't mean Sim A gets to kiss whoever in whom they might be romantically interested in front of Sim B if Sim B does not share those interests themselves.

Sims can have as many romantic interests (RIs) as they want or can handle. It's that they can only have one partner (steady or higher) each, this is where the problems really are. As far as I know, this feature doesn't really work anymore as one of the later patches broke it.

What we can do is keep all of our sims in such relationships at status levels no higher than Romantic Interest (RI), so no steadies, fiances, or spouses, and deploy the No Jealousy (WA required) and Above Reproach LTRs all the way around to help keep things a bit more smooth. Reputations will still likely suffer, though and might require an occasional reset with the Clean Slate LTR.

Don't think I was made aware it wasn't working anymore?