yes heemin run away at the end, because he felt betrayed that iheon knew everything from the start and yet still "confined" heemin to the point of having cctvs all around the house later on.
in their first life, they weren't exactly a normal happy couple, like the book said that iheon was seeking revenge to heemin (heemin's dad took over iheon's company and on the day iheon turned into alpha he was "abandoned" by heemin, it has a whole backstory on that accident and how heemin has alpha's scent trauma)
heemin was auctioned by his step dad after his dad died and iheon took him, he loved him but he wanted to have revenge too. iheon forced heemin to have sexual intercourse to the point of pregnancy even though heemin has alpha's scent trauma (iheon also have digestive issue when he suppressed his scent)
heemin ran away to omega center, there he was chased by iheon and got dragged back to his house, he was under a big stress and got miscarried. after the discovery, heemin tried to suicide by drowning himself in a bathtub but was discovered by iheon.
in their holiday chapter (which is coming soon around 2 or 3 chapters from now) there's a part where heemin fell asleep in a bathtub while waiting for iheon. iheon found heemin in the tub and went crazy thinking that heemin attempted to drown himself like what happened on their first life
iheon is a sole heir to a "gang" like family or company. when iheon tried to take over the company that at that time belong to heemin's step dad, he was caught in a fight and stabbed to death by heemin's step dad and his "gang" partner that has rivalry with iheon's family "gang", after seeing that heemin who miscarried felt there's no need to live anymore stab himself while holding dying iheon on his arms.
english isn't my first language, so excuse my mistake and asked away if something is confusing
so their first life is their life on the book.
heemin miscarried, iheon got killed, heemin killed himself. during this life heemin ran away from iheon to omega center, where he met 3 sisters. on omega center, he drew sketches of life he wanted, family (the 3 omega sisters from the omega center), life without abo, iheon as friend.
on "second life" which is the world that heemin drew, he has family (the 3 sisters), life without abo and iheon as friend. but his sketches are limited up to college life. iheon woke up from "the dead" of the first life on heemin's sketch during their highschool. the world here is miserable for iheon because it's heemin's imagination so when there's no heemin involved, the world stop and the people didn't move even when iheon was there. he endured that for years in loneliness and he knew that the time is running out as heemin's sketches only stopped at their college life. so he asked heemin to go to the us (means their original life from the start) before that, iheon found their book (or it was him who wrote it i forgot) and slipped in on heemin's bag, which was found by his sister and asked heemin to read it as the characters are the same name as heemin and iheon.
cue their life now that restarting from the auction scene. iheon remembered all, heemin knew the plot from "the book" and his memories from the imagination world. when iheon asked if his memories are back, he was asking about the 30 years old heemin (the first life heemin)
eventually heemin got glimpse of his past life from therapy, his "imagination world" sketches and the final blow is that he found "the book" on iheon's safe, that's where he realized that he is the main character of the book. he ran away to the omega center to meet his "sisters". while he was there he was afraid that iheon will chased him down and dragged heemin back (that's what happened on the first life) but iheon held back because he knew heemin will hate him for that. eventually heemin caved in seeing iheon went to the omega center just to do volunteer work and not disturbing heemin (but he gave a lot of gift when he knew heemin was pregnant)