
Short spoiler.... I skipped a lot of details
Basically he keeps counting the number of his regression until 20 cycle then he lost count if them. Because of so much regression he also forgot things about himself, he only remember things about Hyun.
Because of that too he develops anxiety, paranoia, hallucinations and he was very broken inside.
Afte he reveals the truth to Hyun, Hyun promise to survive together with him and never dies again.
In one alternative ending (bittersweet/BE), Youngwon died first and Hyun killed himself to turn back the time. He did it, and when he looked for Youngwon, he saw Youngwon looking like a dead man. His eyes had no hope in them.
When he approached Youngwon, Youngwon tried to kill Hyun because he thought it was another hallucination.
Hyun, after his regression became a little different. Sometimes he forgot this is a second regression, and he became morally ambiguous. He no longer cared to save other people. His world now centered around Youngwon. They barricaded themselves in a building full of supply and Hyun doesn't allow anyone inside. He ignored them practically and saw the survivors getting attacked by the infected and do nothing about it. Youngwon was concerned but Hyun priotised Youngwon more.
For the HE (but still bittersweet to me), they managed to get out. He offered himself to be used to create vaccine. His family was there. They were still in loving relationship after few years. They argued, made out like normal couples although Youngwon had a serious case of separation anxiety and that caused the argument about Hyun workplace. Hyun won btw.
On Christmas together with Youngwon's birthday, he got seriously down with fever and things happened but in the end of the day, they still had intense make out session and Youngwon confirming Hyun whether he was still alive or not and asked him not to die. Hyun promised. He then gave Youngwon rings as present and the end?
(I really want to see Youngwon's laugh illustrated because of the birthday cake. It's so precious)
He suffers so much. I can't wait to read more so I finished the novel and man, I cried for him like he suffers so much.