I'm more and more inclined to believe that *THEORY*
The drama takes place inside a simulation that is been running after a new ice age and that the "monster" that end the whole "world" that is under the temple is actually a "button" that arrest the simulation and makes everyone wake up in their bodies that are being kept in cryogenic sleep. The people in the temple are the programmers that look after the simulation (and they remember the real life when they are inside of it).
It's not really a triangle. She loves the first lead , who loves her back and is friends with second lead (who is in love with her, but it's one sided). It has a cliffhanger ending, not really happy (at least not for all the characters or so it seems).
At the end, when pi talks about the soul, he said that if you copy a human mind into computer it will not occupy any space, but it's there. I think he said that because he did transfer Mama's mind into his servers, that's why at the end he said she could cry and that they are not divided by the screen anymore.
I've seen lots of sci-fi dramas and this is one of the best so far. Unfortunately Asian sci-fi series are usually mediocre, especially ones about AI robots that are basically just there for romance. This drama learned from novels and shows/movies like LOST, Resident Evil, Walking Dead, Maze Runner, Humans ect, so it may be not the most original show, but it still has something to offer in terms of sci-fi, horror, psychology, thriller and romance. I will recommend it even to my friends who usually don't watch Asian shows.