When did the Church insist that a King or nobleman must marry anyone with whom he had enjoyed sex? It may have been suggested generally in public, while a blind eye was turned in reality.
You seem to have a very idealistic notion of history and of the nature of powerful men. There were plenty of royal ‘bastards’ roaming around. Many were even acknowledged and supported.
I have a “risk-assessment” view of what the Crown thought and did publicly, versus what its members did privately. Of course there was copious lying and cheating. It goes with the power territory.