Not Necessarily

Sierra sighed before answering her sister's question. "I didn't realize it until I was dating other people and not feeling a spark with any of them. Mom had to talk some sense into me." 

"Of course she did," Scarlett said with a laugh. "You've always been dense. I called the two of you being a thing ages ago. Any guy who puts that much time and effort into another person has to be in love." 

She had been saying that from the very beginning back when Nathan was only helping her out because she happened to end up on his danger radar so often. He would have done it for anyone because that was the kind of person he was. 

When had that changed? What exactly made him fall for her? 

It was obviously done against his better judgment since he had been so determined to be alone until recently. Maybe all it took was a near-death experience to get him to reexamine his priorities. 

"Yeah, yeah," Sierra grumbled. "Are you done with your interrogation now?"