the fact that uke actually have DID and this isn't some kind of isekai story but his mind is just f up from the trauma
No.
Here's a better summary from manga*updates:
Huimin Seo happened to read a tragic BL novel where the two main characters had both his name and even his best friend’s name, Iheon Cha. But rather than remaining as an incredible coincidence, this book becomes a new reality for Huimin. Before he knows it, he is transmigrated right into a major scene in the novel where Huimin Seo, a rare dominant omega, gets bought off in an auction by Iheon Cha, a powerful dominant alpha. Aware of the complications in this love-hate relationship that he cannot escape from, Huimin must tread carefully to turn things around entirely.
It's good, it's really good. But I don't feel anything after completing this in 2 days. The story feel rushed, abruptly end just like that. I don't see "real" development in their story whatsoever.
This story is fast paced but I think you'd feel differently If you were you read it in one sitting
probably the other reason was because I already read similar setting or plot like this one (two souls, painter of the night, night song and etc) I feel like the way the characters develop are more... felt? idk how to explain