Your cat has my sympathy, too-patience-it will resolve.
When we got Husky girl as a puppy, she drove our cat (we only had one then)to spend most of his day under the bed in the guest room, only coming out when the dog was either outdoors or asleep. that weent on for a couple of weeks. One day, the cat was coming out of the utility room after eating when Husky girl went charging at him. Instead of the usual retreat, the cat jumped at her, boxed her nose and chased her into the master bedroom. Their relationship improved rapidly after that.
I hope that happens soon. The cat was here first. I will protect him and keep him safe until he figures out how they will coexist.