It was what I thought it would end up being: soul mates. Or at least their souls were tied together. I'll admit that the whole soul mate thing is overdone, but that isn't really what this turned out to be. I had the idea that they were soul mates during the first book, with G's comment about how she felt like she'd known him forever. Other ideas came out as the books went on. Not just soul mates, but past lives was something that I only thought about in this book. The idea was considered for a moment in the book before this one, with all the dreams/flashbacks. The idea was basically proven when Roman asked G to get Seth to be hypnotized.
Carter's angel job being G wasn't really that shocking in the end, I'd always wondered why he hung out with the hell-crowd. that would be a good reason. He always seemed very interested in her relationship with Seth.