I had a spayed female long time ago that I tried to bond to an unneutered male. The day I found her sitting in a flower pot to get away from his constant humping is the day I scheduled him for his neuter.
I now have a test that I highly recommend: get a stuffy for your male bun (all my bunnies have gotten one anyway and cuddle with their stuffy even after being bonded). See what the male does to the stuffy. If you want, you can even rub the stuffy over the female's fur first.
I used this test with an unneutered stray I took in a month ago, since he was so good with his litter box and wasn't showing any “romantic” signs or spraying, so I thought I might not have to neuter him. I had to take the stuffy away because he was wearing himself out humping and biting it and getting more and more agitated. He is now scheduled for a neuter in April before he gets introduced to my others.