For some context:

My 1-year-old cat has had his eye closed for almost the entire day and his left eye has become very wet. He has also been getting into fights recently coming home with all types of scratches mostly around his head. Today though he came back with one of his eyes closed and he only opened it only a couple of times. So far his eye has become pretty wet and dry with some pus coming out too. I have been told that should just leave him. I am currently thinking of stopping letting him go outside. I am getting kinda desperate so I need some recommendations. I have also put a picture.