Not the author kinda inserted 'what if' situation where MC ended up with bad 2nd ML, just when we readers finally forgave and embraced the main ML back.
Honestly, I didn't even considered this 2nd ML dude as a love rival, he is more like an antagonist character. Which is why chap 37 caught me out of guard, lol.
Arrgghh why do i wanted to cheer for this relationship!!
Ig the theme of this story is really about REGRETS, from both the main ML & 2nd ML. author nailed it!!