What kind of feeling is this?

RK's car stopped below Stella's apartment, and he didn't drive away for a long time. He opened the car window and quietly let the cold wind blow him for a while. Then, he started the car slowly and left. The car drove on the road, but his mind was not focused on driving. Just now, when he kissed Stella, he had a feeling that he had returned to six years ago. The first time he kissed her was still as familiar as if it was something just happened the day before. God, he had never thought of the moment, when he kissed her in the past six years ago. Why did he just kiss her today, and all the memories returned to his mind like a movie? It was over. He had never recalled those things before. He had never wanted to think about anything after he lost them. That sudden feeling made him feel at a loss. What kind of feeling was that? What on earth was going on? He even began to think that the reason why he was feeling like this was that Stella had given birth to a baby for him. Could it be that