I haven't tried CBD oil, so I'm not sure how it works. I have used Feliway which comes in a spray as well as a multi-cat diffuser that you can plug in an outlet in rooms where your cats spend the most time together. There's information on the Feliway website on how and where to use these products, so they work the best.
Bach Flower Remedies has a Pet Rescue Remedy formula for fearful cats. It's used by adding a couple of drops to the cat's water and could help with the aggression.
You also could try distracting them both with a cat toy before the one cat has a chance to go after the other.
If none of these things work, I would ask your vet. Medication to help calm him is also something that might reduce his anxiety and reaction to the other cat.