Okay, I shouldn't claim perfection. But I've spent years studying the romance arc while you did things like feed your children real food, mow your lawn, check on your elderly neighbor, watch your kids' track meets, listen to your spouse, and ride the stationary bike at the Y. All those hours, I was learning and relearning a romance plot, with part of my mind thinking "grilled cheese sandwiches are fine for dinner, this is art."
And that's important. Because when someone tells you what the romance arc is, at first, you'll hear formula. But it's art. Shakespeare wrote in iambic pentameter. And I don't want to guess how many people told him that was formula and not art. Probably everyone. To this freaking day, a pile of centuries later, we say "He wrote for money." Well, of course he did. But it's still the pinnacle of art because he described human nature. And that's what romance writers do: describe universal human nature in a structure that is thankfully more forgiving than iambic pentameter.
The structure is actually so simple that most people forget it's a structure, but it's the same principle that guided Shakespeare's lovers: 1) two people meet who are right for each other because 2) they will help each other defeat their fatal flaws but 3) their flaws are deep (childhood trauma + society's dictates) so 4) they will be forced to be together and as a result 5) they will either change and grow or lose the love of their lives.
That's it, really. I'll admit, I fudged on the SO they will be forced to be together part but that's the basic structure. The adhesive is a post for another day.
Here's the really cool thing: the romance arc works even if you're not writing a romance. I can guess Shakespeare didn't intend for MACBETH to be a romance, but you can see pretty easily that he understood that Macbeth and Lady Macbeth had fatal flaws that, with each others' urgings, would cause them to lose everything.
And that's where the art comes in. Because whether you're writing about a nuclear engineer whose fatal flaw is mistrust or an overweight, divorced mother whose fatal flaw is that everyone in her life has told her that she's stupid, you're connecting with the best in human nature. You're reaching what can make people overcome those ground-in flaws, and let's not pretend anything but love is that powerful.