Because his mother has him hanging by a thread. And his mother definitely has something against the 'random woman' too. She is a woman of high influence and can harm both of their lovers if she sees fit.
Didn't his mother say earlier that he has to get married if he wants to stay with Meili?
It's quite simple actually :
The girl he is marrying and her family will become business partners and thanks to that union it'll help Ge's business.
It all comes down to money (this kind of wedding really exists)
His mother doesnt care about his happiness, she wants him to get married for a business point of view.
So she threatened both her son and the bride to hurt their significant others if the marriage doesn't happen.
Ge probably thinks that now she'll let Meili of the hook but we all know it's useless.
I’m still not getting why he has to marry a random chick who’s in a relationship of her own. Ge keeps saying it’s to protect Meili. How is getting married going to protect Meili ? The story isn’t really adding up. The story never continues where it ends either.