because he never outright rejected the ex. He keeps trying to force MC to tell him to not see the ex and when MC doesn't do it, he sees him. The ex crashed every date and ML never rejects him strongly
Mate he very obviously has no interest in the ex. There's not a brain cell between the four of them
to us readers, yes. But to MC, for all he knows, ML is keeping a gift that his ex gave him a decade ago, ML never outright rejects his ex, MC already feels some inferiority complex towards ML's ex because that is the guy that MC's ex cheated with (so MC is predisposed to thinking ML's ex is so desirable to these guys). I don't blame him at all to be honest.
Except he's taken the word of someone untrustworthy who didn't even see it. Not a brain cell.
I seriously don't understand why they think he's in love with the cheating POS ex. Y'all pull yourselves together.