Lucyindskye

oh Yay! She's actually my favourite . Started it because of her.

I mean you are allowed to criticise things you don't like. :)
This is a rom com not a thriller, why would the romance be implied? The thriller aspect though drives the story, is not the actual point of their story. It's their tangle ill fated destiny, but I understand your criticism.
I hope at least you enjoyed the rom com part of the drama hehe.

This is how I understood it, you can however disagree :) : He's a serial Killer. We see in his car he has tools for murder and even has a murder den (where he takes sol)
1st Timeline : Sol got kidnapped by the driver simply because she was at the wrong place at the wrong time.
2nd Timeline : This time as she ends up at the reservior, driver sees her alone and tries to approach but there was a drunk man (a variable) thus he couldn't. Next day, that drunk guys' body was found at the reservoir - meaning he killed that guy and since he found sol's phone was there means that she would be a witness/ or simply that she's unfinished business, he tries to kidnap her again but fails ( saved by taesung's dad) and this time Sol actually knows his face so he needed to get rid of her.
So, He again tries to harm her in 2009 (10th May) but fails as sunjae intervenes again.
3rd Timeline: Now since sol goes back again sometime before her "abduction", instead of kidnapping her on 10th may, he follows her to inhyuk's hometown (6th may) but again sunjae intervenes.
In the last timeline, since sol moved away from her OG house, even before the original accident was supposed to happen, he never encounters sol... he does however tries to kill other people in the meantime.
Sometimes bad people are just bad people and do bad things w/o any reason. :)
They did address the bells part in the 2nd time jump though. Since the sequence of events was same ( he broke sol's phone, followed sunjae to the hotel, bell rang etc) it was implied that the same thing happened in the OG timeline.

But they did clarify though? He was a serial killer psychopath, a bad person who didn't need any backstory. He wasn't obsessed with sol, she just happened to be at the wrong place at the wrong time, since sunjae saved her and sent the driver to jail , he came back for revenge. Sunjae never committed suicide, in every timeline he was killed by the driver. In 1st episode we hear the bell ring before it's shown that he fell down.

to be fair, sol hasn't walked for even used her legs in 15 years, she's allowed to be clumsy. :)

I think it will all be included in the blue ray, including BTS and commentary from Hyeyoon and Wooseok. I think you can pre order it now :)