Thanks for the chapter!
I agree with her, MC is an idiot. Rather than agonize about it or ask to break up he should have talked to her about the mixed signals and feeling at a loss after guy told him she's unhappy. Be interesting to see if the twins are going for the two people sharing the same identity aspect or something else. Otherwise it would seem strange that both are sleeping with him for at least a year without getting into an argument or caught fighting about it. Frankly I'm surprised he didn't think girlfriend had a split personality considering how opposite she acts with her sister from what little was shown. Like in first chapter sister is leaving the bed looking cold, serious, and in a permanent bad mood. Then girlfriend is all bright eyed and chipper in the kitchen.
@Akabane I doubt it. Considering he's so drunk he can't even tell he's talking to his boss and not his girlfriend he likely too soused to notice it much less feel it. Best method would be something strongly tied to him that would prompt him awake. Like why's he sleeping around when Ting Ting is in labor with his child. Or since he's a workaholic maybe something like the deadline is approaching fast so how can he be sleeping on the job or something like that.