Nathan > Leia
Nathan isn't quick to get attached to people. They either need to spend a while around him or catch him in an exceptionally vulnerable moment, and Leia hasn't done either yet. First impressions, though? He likes her. She seems smart and nice, and those are good qualities. He likes knowing people who could physically stop him if he snapped and tried to hurt them.
He barely remembers what happened in the hotel. She helped him when he was in a bad place. He knows that, and though the rest of his recall is foggy, that does mean something to him. People who help him even when they have no obligation to get to him. That's why he needed to thank her at the party, and that's why he won't avoid her in the future.