The guy hasn't done anything, though? At least not yet, but we have seen their relationship is strained. If you already see him as the worst, then I guess you haven't read "A World That I Rule" or "Umareru Kachi":
http://www.mangago.me/read-manga/a_world_that_i_rule/
http://www.mangago.me/read-manga/umareru_kachi_no_nakatta_jibun_ga_anna_no_tame_ni_dekiru_ikutsuka_no_koto/
The world that I rule..is terrible..I only saw a few snippets of it and was like..hell to the no's...
on Anniversary you are f...k your fiance imagine another woman and when they ask u abouth a video u became angry I REAPET ON ANNIVERSARY!
His GF chose a wig that made her look just like the other woman. He can't exactly help that that popped into his mind, can he?
The whole act of sexual cosplay is, at its foundation, being someone different. Why condemn that?
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He was angry at how distrusting she was of him. She was glaring and scowling at him the whole time he was trying to explain:
"Then why did this person upload the video?" What the hell kind of question is that? He can't speak for some anonymous person's motives. This is just rhetorical, laden with an unspoken assumption against the MC: 'Then why...if it wasn't true?'
"Why didn't you tell me about this?" A legitimate question, but look at the face that's asking it. That'd make anyone feel defensive. There are plenty of possible reasons, but before he can even answer she hits him with: "If you're innocent why did you have to hide it?" Bam, guilty verdict, defendant may not speak! How do you even begin to answer with that kind of setup? 'Well I was hiding it because...' Why is it suddenly assumed he was hiding anything? Talk about a presupposition. Not having mentioned something yet does not automatically equate to intentionally hiding it.
"You looked at her. That's why she misunderstood you." She wasn't there, and the video was taken from behind him, so this is purely a wild accusation. She's just laying into him, not caring about his responses.
She's a flight attendant, and it's clear they don't see each other very often. Their communication will of course be limited by this fact. The strain of that separation seems to have worn down both of their patience for each other.
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He's certainly skirting the line, but he hasn't crossed it yet. Given this is an adult manhwa, he probably will eventually, but right now I wouldn't call him "the worst".
I know, i think is best for both them to separate.
MC is the worst,
actually all mc in yomanga is the worst, except sweet guy