Is normal that a guy goes really bitter after rejection?

I have a brother and he is 20 years old. I would say he is pretty good looking. I know about many girls who were crushing on him. He had one relationship but it didn't last too long. Now he was really into one girl. She liked him first and had crush on him for a long time. They were seeing each other for some time. I know they kissed few times and dont know if anything more. It looked like they will be couple really soon. But then she rejected him. No one saw it coming. It really hurt him. It happened seven months ago. He says he is done with dating. He could have more girls if he wanted but he just looks so uninterested. He is really bitter towards dating and couples. He spends time only with his friends and drinking. He plays soccer and almost all guys he plays with are like 28 years old single guys. I am kinda afraid he is becoming like them. My brother was always ok being alone and single. He always wanted to travel on his own but i just dont want him end up alone cuz i think he is good guy. He treated that girl well, he was nice, kind and sweet to her. But his attitude now is really bad. He is like what is the point of dating and why would he do it again to himself.

Is normal that a guy goes really bitter after rejection?
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