I don't know if it will be the same for you, but for me, once I cut my portion sizes down to what they should be, the first week is very hard. I need a lot of will power to keep my goals that first week. The second week it gets easier, and pretty soon my body seems to adjust to smaller meals. I go from being able to eat 4 slices of pizza to getting filled up with one.
I have snacks built into my meal plan (mid-morning, mid-afternoon, and evening) so I never have to go too long without food.
Use "tricks" to remind and distract yourself. Put your food on a smaller plate so it will look like a full plate of food. As soon as your done with a meal, brush your teeth. In between meals, block the entrance to your kitchen with a chair that has a sign on it saying "Do I really want to eat now?" or "60kg by June 1" or whatever might dissuade you from going into the kitchen. Post a list of distractions for when you're tempted to eat (call a friend, go for a walk, take a bath, put some music on and dance, etc.). If you have alternatives laid out, you don't have to think too hard - just pick one.
Congratulations on sticking with the exercise so long! You must be very fit. Just use some of that same determination you used with your exercise program to master portion control.
Age 61, Height 5'9"
March 2010 145 lbs, Jan 2013 173 lbs
1st Goal 145 lbs 5/25
New goal 140