See the TL pointing out that "sleeping together" is not a euphemism actually does change the context a great deal. Iino wants to be able to share a bed with Rintaro, but not actually "do the deed." But if Rintaro can't control himself and wouldn't be able to avoid escalating, that's obviously a bit of a problem. Hence, the test of his sexual restraint to prove for the both of them that Rintaro can restrain himself enough to be physically intimate with Iino without trying to force sexual intimacy in the process.
