I’ve always figured it would be a Regina/Henry kiss that broke this Curse, so that didn’t surprise me. But the whole time I’d been thinking that, I’d been thinking that Zelena had cast the Curse, so blood magic whatever and that’s why Regina. But that doesn’t hold water any more.
It could just be that it had to be someone who was cursed had to kiss someone who WASN’T cursed, and that connection would break it. That would fit for Regina and Henry.