You have my sympathy, Mongoose, as you face an unpalatable choice no matter what you do. That said, I agree that your best bet is probably to withdraw your forces from eastern Turkey and fortify Nicea & Trebizond. The lands of Italy and Sicily are too rich to simply abandon; and as you yourself pointed out, letting them go might open the way to a Papal invasion of Greece.

I would try and keep a decent garrison in Antioch if it's at all viable -- given both the prinicipality's wealth and strategic position, it's worth holding onto if you can manage it -- but otherwise I wouldn't hesitate to get the rest of your troops out of eastern Asia Minor and use them to reinforce Nicea/Trebizond/Big C.