My cockerel is attacking my one pullet

Hi,
I have a 22 week old pullet and a 22 week old cockerel (about that age). The cockerel is just getting to the age where he wants sex I think and up to now they were like soulmates, the perfect chicken couple now my pullet looks so depressed, in the past few weeks she has been clucking a lot, what does that mean ? Also yesterday, I have seen my cockerel bite my pullet on the back of the neck and shake her head around about 5 times, my parents say that its natural but I understand I should really have at least 6 chickens for it to be fair. I have 3 chicks growing up, the farmer says that I can let the chickens and chicks live together in late November when they will be big enough to get into the pecking order and be strong enough to stick up for themselves. Right now I am worried because last night she got pecked by him again on the neck and he stopped then she just put her head down for about 20 seconds then lifted it back up. Did he injure her or is she just depressed ? I really want these chicks to grow up fast because I am worried about her dying from sexual exhaustion which I have heard of happening on the internet.

You may wish to consider isolating the roo for a while and give the girl a break.

Is there any particular reason why you want to keep the cockerel? A flock can manage just fine without one.

However if you are intent on keeping him you may need to seoarate him until the younger pullets are close to laying age. Otherwise he will endlessly harass your older pullet.

Having only 1 hen and 1 rooster isn't a good idea. Roosters need multiple mates or you end up with an overmated hen. If it were me, I would either rehome the rooster or separate for now. I have 10 hens to 1 rooster, that's minimum from what I've read/heard/been told. I'm planning on getting a few more hens, but probably not until spring.

Oh, also, my rooster was NOT very gentle at first when mating, and my hens protested loudly. He figured it out within a short period of time now, and most of the time the girls don't protest too much anymore. A couple still do, but the rest don't (the 2 that do haven't started laying yet either, and just seem less mature even though they're the same age as the others)