Their relationship before and after regression?
They used to be best friends in the past. That has changed after MC fell in love with ML and went overboard with his obsession. He used every opportunity and connection to have him. It forced ML to draw the line. They were no longer friends anymore. Beside guiding, they didn't have impactful interaction. Not even friendly conversation. That bring us to the scene when MC was dying. The sudden realization and regret of everything. So far, we only see MC's POV but actually ML also lived his life in regret. For 10 years after MC died, he tried to create "miracle" (mentioned in chapter 2) to bring MC back to life. Only MC's memories intact, ML still have no idea at all. During this 2nd chance of life, MC trying his best to do everything to make Woojin happy without manipulation, without anything shady. He is genuinely trying to change their future relationship. Not only Woojin, but MC also trying to do his best to save everyong from the upcoming terrorist attacks from organization named Black Swan. He basically throw himself into danger every single time to save people around him, including Woojin. When Woojin start to fall in love with him, he still trying to surpress his feelings because he thought it's just temporary. He thought Woojin will end up with Nam Haesol but this is not true. Woojin and Nam Haesol also strictly just guiding. No romance at all. But Woojin did team-up with Nam Haesol (in the past) to fool his step-mother. His step-mother is evil person trying to take down Woojin too. Not take down as in to kill him but his step-mother scheming something behind his back. Unfortunately in past life, his mother and MC worked together. That's why ML in the past life distancing himself from MC. Their relationship was full of misunderstanding. From both sides. Almost everything resolved much later after Jaechan confessed that he went thru regression. But that time Jaechan didn't tell that he has died. ML kinda can guess what happened to Jaechan before regression took place but both couldn't expressing their words. ML growing much more protective, not in a bad way at all. He was and is gentle human being after all. He is a green forest. Their relationship going smooth and all lovey dovey until the end of main story. This is a slow burn, meaning all lovey dovey scenes will happen much later. Much much later. In the novel I think it took 2 years after regression. Beside their romance, the action scenes are superb.
I'm reading the novel (now reading the sides), and holy sheepers. I'm bawlin like a baby on the last few chapters. Like these two babies, just TALK! but still, I'm so, so, glad you two got this chance again.