I don’t know how mature your hens are or how mature the roosters are. I don’t know how much space you have, the personalities of your chickens, hens and roosters, your management techniques, how long they have been together, or many other things. You could write books about that and most of it will be opinion anyway. Each chicken has its own personality and each flock has its own dynamics. The best we can do is guess based on our experiences and sometime I guess way wrong. Our situations are all unique. Each flock has its own dynamics.
I always suggest you keep as few roosters as you can and still meet your goals. That may be none, one, or several. That does not mean you are guaranteed problems with more roosters, just that you are more likely to have problems with more.
I am not a great believer in magic hen to rooster ratios. Some people keep flocks with very low hen to rooster ratios, some people have problems with one rooster with 20 to 30 hens. Each situation is unique.
I don’t know why that rooster has fixated on that one hen but he obviously has. It may be something that fixes itself with time or it may not. I could make some guesses but it’s probably not important. They’d just be guesses. I think the other two have given you some pretty good options. What you do pretty much depends on your goals and why you want roosters.
