Need help with a dominant 8 year old male cat

[u/The_Omen17]

I have a 8 year old diabetic male that became diabetic about 8 months after getting a kitten. For the most part they can exist together, but its never anything more than that. At worst he'll chase her around the house and if he gets ahold of her he pins her down. I think the added stress of the smaller female cat in the house is worsening his Glucose control. Is there a way to get them to get along? Sometimes she'll jump up on the bed where yes laying and try to lick him, to which he just starts smacking the shit out of her lol. Sometimes there's fur but never blood etc. Its never terrible just bad.