That must be something to see. It does sound comical having such a small squirt decide this giant girl should be his for the taking. However, his compulsive behavior, fixating on this one gal, is sending up a red flag.
As you suspected, his pestering may be escalating. Roosters are capable of seriously injuring a hen that refuses to submit. They are capable of rage. You may want to nip this in the bud before she gets hurt. Let me tell you a true story.
It was a few years back that I had a hen that my younger roo was fixated on. Toots, the roo, decided Geobett the hen was going to submit to his advances or else. But Geobett, being eight years at the time, didn't want anything to do with him. She avoided him. She ran from him. But one day he had had enough and managed to chase her into her run where she lived with another hen apart from the flock.
Geobett ran into her coop and Toots cornered her there and ripped her scalp almost all the way off. When I found them, Geobett was bleeding heavily and Toots was still trying to force her to submit. I chased him out and took her away to get some extensive wound care.
I made sure that Geobett was safe from Toots from then on. She would only get to free range when Toots was confined. Most of the time Geobett was content in her run. Not so the fanatical Toots.
He would spend a lot of his time growling at her through the run fence, and he could get so worked up in his rage he would attack the fence trying to get at her. In the process, he would get shocked by the lower hot wire running around the run. This would further enrage Toots, and he would attack the hot wire that had "attacked" him. He seemed demented by his rage.
This went on for weeks until one day Geobett died in her sleep from a reproductive infection. So, this is what a rooster spurned can do. It isn't pretty. Don't wait for your half pint to inflict serious injury on your pullet before you do something.
