so, i think this is what really happened

this is just my understanding ok!!! feel free to correct me if im wrong. it can be a bit confusing too, since it is not mentioned directly but:

dojoon = he doesn’t have 'romantic' feelings toward the tutor, he was just really close to him.
haeyool = has a romantic feelings towards the tutor.

after dojoon and jaewon got hit with a truck:

dojoon went back in time 13 years ago when the tutor died. he made the same decision back then and live through his past again (as a 30 year old something mentally or maybe physically as well?).

then he met jaewoon who thinks he transmigrated jnto a book (because the last thing he remember thinking about was the book that dojoon handed back to him when they bumped into each other in the crossing??)

so, what really happened is that both dojoon and jaewon went back in time because of the book. they just think they're in different circumstances. dojoon thinks he went back in time 13 years ago, and jaewoon thinks he went inside a book (this is why he probably can't find the female lead?? did he find her? i dont even remember)

SPOILERRR:

I've skimmed through the novel before and honestly the regression part still confuses me but in the future events in the novel, jaewon and dojoon eventually goes back to the real life present times. jaewoon wakes up from his coma and iirc dojoon goes back to a different point in time and he spent actual years looking for jaewon. or at least that's what i remember!!