Jinnah was prepared as late as July 1946 to accept a United India but there were other forces at work too. Some put attribute the partition to Hindu aggression, others to muslim insecurity and some to British divide and rule policy. I believe it may have been an amalgamation of the three.
Wrong interpretation of historical perception.
Jinnah was an astute politician and knew his moves and the resultant outcome much better than many perceived. His offers were provisioned on certain acceptances by the Congress. He knew that the congress would never agree to what he sought and his demanded provisions were thus rejected by Congress. Thus, those Muslims who were skeptical about creation of Pakistan, better understood Congresses motives and started supporting him. Those English decision makers who were also reluctant to grant their support for creation of Pakistan, finally agreed to the fact that there was no other option but.