It’s clear that the thread has nothing to do with affecting how they like each other. MC and ML had the thread tied, and yet they both didn’t fall in love at first sight due to it. Just the fact that MC fell for the blue dude, and the blue dude didn’t, shows that the thread doesn’t do anything for love. It wouldn’t make sense for him to just like the brother only cause the thread is torn.
The thread most likely is just something that makes two people meet multiple times in life, in which provides opportunities to make the pair fall for each other- not that it actually affects their emotions.
I need that thread to connect with that hyung, how the story would flow