AU explanation

In a world where we pretend Daichi's birthday is on 26th of january, people are attached to their soulmate with a red thread, which turns visible for them when they turn 18. Suga's birthday is so close but he is backing away from his own feelings and pushing away the past. He knew that by Daichi's words, Michimiya was his soulmate. But was she really?
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There is no anime or manga spoilers. I haven't even read the manga. If there's anything that doesn't add up I am so sorry!
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The characters do not belong to me.
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Also I am sorry if some parts are quite messed up, english is not my first language but I gave it my best shot!