He eventually finds out when Tsukina use a country-size barrier magic (also the other savior girl die, or at least get close enough that 'God' could recover her)
He even wondered aloud "huh, I really should've noticed this earlier, given your level of magic power in contrast to your lack of common knowledge"
And he plan to keep it a secret, because polygamy is allowed in this country and many people would definitely want to be her consort for the potential benefits it can bring, and Ill want her to be his alone.
It's in ch 12 btw, and the end of 'arc 1' ( arc 2 should continue this Winter...assuming it's not delayed)