I have a bunny who was fully adult when he was neutered. I had him neutered because he developped a serious crush on my dog. He pursued her every waking hour, he circled her, nipped her, never left her side. We tried to block him from her, it made him madly unhappy and he frantically tried to gnaw through the baby gate separating them. He didn’t get a moment’s rest, poor darling.
2 weeks after the neuter, he’d forgot about his crush. He also stopped per-and poop marking her spots on the sofa and her own bed. That took a bit linger though.
I don’t know if all bunnies react like my Bam, and he never showed a romantic interest in anything or anyone but my dog – but having your bunny neutered is your best bet imo.
Some bunnies get worse hormonal wise for a period after the neuter -that’s known as a post/neuter craze. It generally subsides after 1-2 weeks.
Since he’s an adult, he might recover a little slower than a very young boy does. I had to syringe-feed my Bam pellet mash and give him a hot water bottle to snuggle up to. He was all right again after 2 days.