I like the scenario! It sounds really good!!

As for the attraction thing between supernaturals, I think the whole "angel having a fallen angel as their opposite" idea is great! 

And then for the romance, that can also explain why they would attract, hence the whole "opposites attract" saying when it comes to love I guess? I like both ideas, and i think that the second idea would be better, buuuuut that also depends on this too:

When they realize of their supernatural-ness, is it like a whole "Ugh I found out that you are my sworn enemy, now I hate you forever because it was always a thing even though I forgot and thought I was human" kind of thing, or would it be like a "Oh gosh, I am a supernatural being, and we're supposed to be enemies but I always thought I was human?? What am I supposed to do about this?" 

Basically, would they strictly stick to their sides when they find out, or would they be conflicted? Or would that just depend on the character? I feel like Abigail would try to stick by the rules at first, but then she actually starts feeling bad for just shutting Roman out when he had actually showed that he had some good in him or something (and also have a small crush on him). 

I guess it could go either way... But the second one would be interesting to watch, and it could give us opportunities to do fun things with the two maybe? I don't know, it's late and I'm kinda sleepy TuT