Ain't no way

Shuichiro have all the rights to refuse to have sex with ML bro. Like what do you mean prove your love by having a sex or doubt your love because you don't want to have a sex. That's a no-no.

Shuichiro is obviously being reserved for that intimate part because he's unsure how ML really feels for him despite the sweet actions-- it's always being contradicted by ML's constant persuading to have sex. That's why.