I recently had the same dilemma with my kittens, with a similar result described above by Golden Kitty. The vet assured us it was okay to leave them together as Alex had been neutered two months before, and at first he expressed some interest in satisfying her condition but quickly lost it. My BF described his reaction as that of a man running into a girl he met briefly and never wanted to see again; he looked at her indifferently or like she was out of her mind (which I suppose she was, in a way). She was recently spayed and everything has returned to normal. Good luck with yours!