Hmmm, sometimes bonded pairs will go through some periods where they reestablish their dominance.
When he follows her, are his ears forward or back? Tail up or down? Ears forward and tail down means he wants to mount. Ears back and tail up is aggressive.
First I would rule out a medical problem with one of them. Sometimes one isn’t feeling well, and it affects their bond. With Bertha and Moose, when Moose was having dental problems, Bertha would chase and bully him a bit (sad, right?) because he wasn’t being as affectionate towards her.
Do they still cuddle and groom a lot? Has there been an uptick in marking outside their box?
Ruling out medical issues, the next thing I would do is “couples therapy”, which means doing some stress bonding sessions with them, and maybe even a marathon in a neutral space to re-cement them.
.
.
.
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.