if i remember right,it is about two high schoolers, were the the dark head like the blonde. who think just broke up with his girlfriend. anyways soon in a drinking session. the dark head confess and have sex but e think it was dream but it wasn't. the blonde wait for him to confess but doesn't. and soon after a girl get in involved. blonde then pretend to question him for a test in computer. and the blonde tell him the truth.

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no it's not this mangaka