He honestly didn't know whom to choose if it happened in reality.
No matter who he chose, he would hurt the other, and there wouldn't be a complete Gu Ning if either of them was absent.
He wouldn't stop loving Gu Ning even if she was incomplete, but the condition was that the other incomplete Gu Ning didn't exist.
After that, Leng Shaoting told Gu Ning about his conversation with Tang Aining and Gu Ning in the illusion. Gu Ning felt a little uneasy when she heard the whole story.
In fact, she was willing to admit that she possessed Gu Ning's body after Tang Aining died. After all, she never planned to keep it a secret from Leng Shaoting forever, and she had already told Shangguan Yang about that.
She just hadn't told Leng Shaoting yet. Since he was aware of that now, she thought that she could tell him everything about it.