beta
You people may find this icky, the ML didn't have much of a choice and he wanted to keep her alive. Marrying her was the best he could do to keep her safe. He did treat her as a child and wasn't planning on keeping her forever but that changed when had her coming of age, so she is now considered an adult at the age of 15, two years passed and she is now 17.
In technicality, this is no longer a minor married to an adult.
He didn't groom her, he took care of her and started seeing her as a woman later on.