I just had a niece (in high school) get shot down in flames after expressing her feelings to a guy she had a crush on. She confined herself to her room for two days and had a meltdown. She's OK now, since she's finally got her feelings in check. But at the time of the meltdown, her feelings were overriding any logic.
And while that's a bit of an extreme case (a two day meltdown for fuck's sake), in BaDIK, the mc had pretty much fucked both girls, and then he finds out they are already in another relationship with each other. So his logic took a back seat to his emotions.
Emotions are powerful things. People actually commit murder when emotions are riding high, so even if the mc was a fucking hypocrite (depending on your play through, my mc was pretty much
fucking everything in sight), it doesn't mean he didn't have any emotional reason to go off the deep end for a bit.
I personally didn't like his reaction, simply because he was being a hypocrite (he'd been making out, getting hand jobs, boob jobs, blow jobs, foot jobs, having anal sex, normal sex, eating out, sexting, groping, fingering and holding the hands of up to 16 other girls at the time).
But I have to go on the record and say I was never in the position where I was fucking two girls and then found out they were already in a relationship with each other, so I can't say that I wouldn't have locked myself in my room and had a meltdown for two days. I'd like to think I wouldn't... maybe 1 day max...