My cat keeps harrassing my other cat? Very weird situation.?

Okay so I have a male cat that is constantly messing with my female cat. She can be walking through the house when he pounces at her and she runs. She is terrified of him, and never fights back. He chases her under the table and sits and stares at her so she can't come out! He also is alwayss looking for her. He never messes with any of my other cats, just her. I try to chase him away but he keeps messing with her. Its very weird ive never seen a cat like this and its not a territorial thing because shes never near him. Does anyone know why he acts like this? Im so upset with seeing her scared that im considering getting rid of him although i dont want to. Please help. thanks!