The Love of Parallel Universes

In the parallel universe, compared to our universe, there are other people alike. Yan Alai from the parallel universe came to our universe after the death of her boyfriend Ye Xinghe. While looking for another Ye Xinghe, she accidentally found herself dead in this universe. To comfort Ye Xinghe's emotions, she pretended to be herself in this universe. When she was kissing him she was attacked and, fortunately, she prevented the attack and gained the trust of Ye Xinghe. However, why did the killer kill Yan Alai from this universe? What is the purpose of the legendary virus coming from the parallel universe? What is the end of Ye Xinghe and Yan Alai in this universe?