Activate your ancient setting mind. There's nothing wrong for an adult man (in the ancient Chinese era) marrying a 15 years old girl (which is a marriageable age). Also there's nothing wrong for the ML to keep an eye on the MC practically for 10 years before he got to marry her. Hubby gotta keep future wifey in the palm of his hand or else someone will try to steal her, no?
ML is a sucker for MC. Their scenes together are so adorable (and naughty) if you don't consider their age differences (again, turn on your ancient era mind). The kissing scenes tho /Lord/
Ps. Forget all the antagonist characters, the one that needs a beating is the emperor. The empress deserves more than him ugh somebody kick him for me.