This is a long story but I’ll try to keep it short. Last November, we got Michael and Gabriel (both male, neutered, pre-bonded) from the rescue. They seemed happy, although we noticed that Gabriel groomed Michael often but not the reverse. One day, after two months, I came home to bunny fur everywhere – it seemed Gabriel had decided to go for dominance, and from that day on, he tried to attack Michael at every opportunity. We tried everything to stop them fighting, but on the advice of the rescue and the vet, we very sadly gave Gabriel back to the rescue. (I’m happy to report that he found a new home with a nice girl bunny!).
We then got Lila (female, spayed, and about the same age as Michael – a year). Bonding them took several weeks but didn’t involve any fighting. They have been reasonably happily bonded for 9 months now, although again Michael often refuses to groom Lila (but will do it occasionally) and has started humping her, which she normally barely tolerates. A month ago, I once again came home to bunny fur, and it had been a serious fight because Lila had quite a few bites
We took both of them to the vet (together), and gradually things improved again over a few weeks. Two nights ago, Michael tried to hump Lila, and she nipped him for doing so. He fought back, and then they were circling and biting. We managed to separate them. We have one pen, and we’ve been taking turns having them in it, as whenever they are out together now they fight – both seem to be going for each other, although Michael more than Lila 
I would love your suggestions as to how to proceed from here. We don’t want to lose either bunny, but I think they are miserable as (effectively) solo bunnies but miserable when they are together. Nothing changed in their environment as far as we can tell. Michael was trying to mount Lila more and more, though, so maybe Lila finally had enough. Do you think they can be rebonded? I am scared of letting them spend time together because Lila has already been injured once
Any advice would be most welcome – many thanks!