Buns will pee for political reasons, marking territory, or their bladder is full and they can't hold it anymore.
And when he's in the litter box, lavish on the praises telling him what a good boy he is for using his litter pan. Rabbit ears will recognize your tone of voice.
A friend has a 6+ yr. old neutered male who persistently pees right outside of the litter box, never in the box.
And we all know of rabbits who use the litter box meticulously.
Had a foster gal that would poo outside of her freshly cleaned litter box for a day or so, then after it acquired a couple more poos, she'd revert to bathroom duties inside her l/pan. So we learned to keep a couple fecals inside the new pan to encourage persistent toiletry habits.
I hope you can decipher why he's soiling on your jeans only. Perhaps place a thick towel on your lap; a baby pad or absorbent product for humans with weaker bladder muscles. Any other pet scents in the home that he could smell on your jeans?
Whew, you'll be happy I'm sure when his hormones subside.