Rabbits love to pee on soft things. Even ‘perfectly’ litter trained bunnies will often be tempted by a bed or sofa. I would say my bunnies are litter trained, but about once every couple of months, one of them will pee on the sofa for no reason I can see.
Rabbits do have a post neuter surge, where their behaviour often gets worse, but it shouldn’t really still be going on 6 weeks after.
They are also especially tempted to mark things that smell strongly of humans, like beds and sofas. One solution is to have a blanket that your bun normally lounges on, so it smells strongly of him, and lay it over your bed. Hopefully that way, the bed will smell like him already and he won’t be tempted to mark it.
The other solution is just to keep him off the bed. It seems like an easier solution and is much less drastic than returning him to the rescue. Please give him a chance, and understand he’s just being a bunny.