A lot of breeder pens are 2 hens and a rooster. If you don't see aggression or over mating, it could be fine to keep your lovely fellow.
Just a side note, coming from my background experience. The best thing, imho, to integrate a new rooster is his broody mom. They thunk sense into the boys head, then as the mom integrates the boy into the flock, the others keep him in check. Dad sees the youngest as a part of the flock. There can be some tussles as the young son matures, but it is soon settled (unless the father or the son are especially aggressive...but dad is only around because he is fine tempered in my flock).
So because you separated, the established rooster sees this youngster as a strange male and is pulling out his tail feathers. That could settle down, or not.
So if your pretty male is doing okay, not acting like a raging hormonal teen with the 2 RIR hens, let him stay and keep a watch.
The only time I've ran into trouble is letting a cockeral remain with a banty brooding hen (his foster mother) and sister siblings. He began to get aggressive with the pullets and transferred that to the poor banty mom...all were in grow out in the separate brooding pen. Though he was pretty, I didn't want his genes in the main flock competing with dad's, for breeding goals, so he went to freezer camp though he was a pretty boy.....he was going to end up killing the banty if he remained....no place for him. Just his luck of timing and genetics because he would have been trained by dad and the hens should he have been introduced into the main flock younger with mom. I've not had any trouble with younger cockerals introduced that way.
LofMc