Gu Xiaonuan and Si Yuchen haven't had a fallout over the divorce issue, but they're not far from it.
Si Yuchen is still giving Gu Xiaonuan a chance; if he hadn't, they probably would have argued a long time ago.
Si Yuchen doesn't need to give Gu Xiaonuan the opportunity to talk about divorce; he could choose any other way instead of letting her have the chance to say so many reasons for wanting to divorce him like she does now.
Gu Xiaonuan has her own reasons as well. Her reason for wanting a divorce from Si Yuchen is quite obvious; it's because she doesn't love Si Yuchen.
Not loving him is why she won't continue maintaining their seemingly simple marriage relationship with Si Yuchen.
Now, Gu Xiaonuan won't continue to maintain this layer of relationship, especially since Si Yuchen has nothing to do with her anymore.
She can be with Si Yuchen, but she cannot deceive Si Lingtian together with Si Yuchen while simultaneously causing Gu Xijue to misunderstand her.