May be i reading too much than it is actually portrayed
In the last scene of ep 12, where so bong confront Human Namshin, He looks at her measuringly and repeats the same dialogue he told Namshin III. But i found his voice much softer comparing to other times.
The moment she talks about Namshin III , there was a subtle change in his facial expression
which kinda felt all she cared about is only him (Namshin III)...and he asked Yena to leave the place.
I am not telling he is falling for her..but just felt he is envious of the strong protectiveness she is showing for Namshin III, which no one has showed to him (Human Namshin) so far.