I love these ideas. The relationships really need to be more dynamic.
The way jealousy works makes it impossible for any sim to date casually without making their romantic interests upset. Unless they complete the serial romantic aspiration, but I don't want all of my casually dating sims to be serial romantics. Sometimes they're focused on their career or are just too young and don't want a heavy committed relationship. So sims with a low to mid-level romance bar shouldn't be so heavy on the jealousy.
I would also love some kind of faithful toggle, too. I hate that if they're both flirty and you choose the right interactions, you can eventually woo pretty much any sim into cheating on their partner, even if they're in a perfectly happy 100/100 relationship already.