I’m sorry to hear this.
What you are describing sounds to have gone beyond dominance and I would be very concerned for their bond, I’m afraid. A fight and what sounds to be bullying (the fact fennel has been contained by thyme) usually means the bond is dysfunctional and possibly broken.
Hormones rising is a reason and that can bring about incompatibilities between them.
In this situation, you should separate them now.
Keep them apart for several few days to allow them to calm down.
You can decide to attempt a neutral territory reintroduction after they have been apart for several days. This will allow them to decide on the future of their bond.
If their bond is functioning, then they will go back together (although you while expect mild dominance - mild chasing and humping).
If during the reintroduction they fight again or if there is any tension or any bullying then sadly their bond has failed and a separation would need to be made permanent.
If during the days they are separated Fennel perks up and appears happier to be away, then that alone is unfortunately a sign of bullying and that the reintroduction is highly likely to fail. You can also decide to not attempt to reintroduce based purely on fennel’s reaction to being away.
Thyme’s behaviour during the separation is not your gauge of the situation - is he likely to be upset by it but you have to ignore the way he reacts to it. If thyme is doing the bullying and instigating the fighting then any insistence on getting back to fennel is usually just a desire to fight again
I’ve added a guide in below to help further
Bonds In Trouble
Bonding and Interaction: Illustrated Bonding Dynamics and Behaviours
Boars: Teenage, Bullying, Fighting, Fall-outs And What Next?
