normally when an author wants to ruin a nice and friendly character they usually go with the MC overhearing some random person going "OMG did you hear? He's a total playboy!" and then show the guy having sex with someone else even though he's single and everyone reading ends up hating him and rooting for the ML
normally when an author wants to ruin a nice and friendly character they usually go with the MC overhearing some random person going "OMG did you hear? He's a total playboy!" and then show the guy having sex with someone else even though he's single and everyone reading ends up hating him and rooting for the ML