You are correct it was the third interpretation.
1. In the present you can see that jinwoo isnt actually that chained up with his work. His company didnt requires him to work late, he can go home early and he has a lot of leave day save up.
2. The author constantly showing the difference between unchanging candy and changed jinwoo. Both candy from 10 years ago and candy from 5 years ago has almost the same dialog when they first appear and jinwoo himself has repeatedly mention how candy didnt change at all.
3. Small instance also with 5 years ago candy ordering chicken for 2 days repeatedly and jinwoo asking if he isnt bored eating chicken and they should order others stuff instead
4. Its also why the author draw the supermarket scene where jinwoo said that he didnt like a certain snack anymore because with time people change but candy still like the same snack after 10 years.
5. Jinwoo himself also mention in cp.17 that him being tired has only been an excuse.
Jinwoo has taken candy feeling for granted
I can’t help but feel like a breakup will be inevitable in their future. They’ve met when they were young and Jinwoo lost the passion of their youth unlike Candy so they became incompatible and that’s that. Only Candy’s investment and the comfort that comes with time are keeping them together at that point
┗( T﹏T )┛
I wish Jinwoo's feelings were more fleshed out. I just feel like their break-up could be interpreted in mainly three ways:
1) Jinwoo really had been exhausted by his work and because of that heavily neglected his relationship
2) Jinwoo was depressed. I feel like most people by now know depression is more than just being sad, but rather it's also a constant sense of tiredness and exhaustion. So I almost feel like Jinwoo constantly saying "I'm just tired" to Suhyeok must've been intentional by the author.
3) He just stopped loving Suhyeok. Ten years is a long time for a relationship and Jinwoo just simply slowly started to stop feeling the love he used to. Their time ran out.
I'm leaning more towards thinking the third interpretation is the "correct" one, and I know I'm not the only one to think that, which kind of makes the ending fall a bit short for me. The whole theme of the story is the classic "you didn't know what you had until it's gone," but like . . . Jinwoo did know what he had. That's the issue. He just didn't want it anymore So I would have liked to see more of inside his head, to see just what he was thinking, why he was so withdrawn from his relationship in the first place