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Neither the MC, nor the ex did any wrong. The MC is in a coma and that is not anyones fault. The ex tried to look for the MC for almost five years but only manage to find his camera and have not heard any news of the MC's whereabouts during those time.
In terms of traumatic experience I think it is the ex that suffers more because while the MC is in coma, he is looking for him and suffering for 5 years but for the MC its only for a moment.
Should the ex just dump his new lover because the MC returned?
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Well the ex needs to act cold towards the MC because his new lovers wants to (he is jealous of the MC). And the ex needs to act cold with the MC in front of his new lover to make the new lover feel assured.
(SPOILER)
In this story, the ex is the one that suffers most, not just because of what currently is happening but he is manipulated by his new lover.
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Thats a shitty thing to do, don't you agree. To throw away someone who stayed by your side because some else return. Btw they dated for only 6 months but the new lover stayed by the ex side since the start, the ex just keep declining because he is still looking for the MC and hopeful that he is still alive.
(SPOILER)
The new lover is the real shit.
uhhhhhhh yo mans just went through a hella traumatic experience and still has feelings for u and this is how you act?????????? WHAAAAAAAAAAAAAT AND WHAT HE LEGIT DID NOTHING WRONG HE WAS IN A COMA BRO WHTH IOWAFJ WFHIFHSAIH