Unfortunately bed-peeing is a really common problem with buns. Beds are soft and smell strongly of humans, so that triggers many bunnies to pee on them.
The most effective solution is to block access to your bed with an x-pen. You could try doing this temporarily at first to see if that helps him break the habit.
Another solution that a BB member had success with years ago was to put a plastic shower curtain under a thin blanket on top of all the other bedding. This had the double function of blocking the bed’s smell (so the bun was less likely to mark), and it made clean-up much easier if the bun did pee. It might be a little annoying to deal with if you are currently in the bed though!
I let my buns free-roam most of the day but I pen them at night, so hopefully you can figure out an arrangement that works for you.
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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.