I think his friend are just concern for seme

Cause they think Rei is a slut or playboy base on what he said "you can do anything", they might be worried of their friend might end up heart broken, and they misunderstood Rei, while Seme also an idiot, who didn't clarify that he has feelings for Rei, while Rei might be hesitant to confess because he thought Seme has already someone he likes