Simultaneous movement

[merlinme]

Could somebody explain to me please exactly how movement is worked out when two enemy sides are trying to move into different provinces?

To give the exact example:

Turn one: I attempt to move into my enemy's province. He attempts to move into mine. We fight a battle in my province. I win.
Turn two: following losses from the battle, I decide I should stay where I am and recruit/ summon some reinforcements. He invades my province with a smallish army, kills my province defence, and besieges my fort (without being able to damage the walls).
Turn three: I break the siege and crush his army.
Turn four: I attempt to move into his province; he attempts to move into mine, and we fight a battle in my province. I win, but it's starting to feel like turn one all over again... Am I ever going to be able to break out of my province?

If I remember the manual correctly, is movement in a random order? And in fact I think it said that, depending on the size of the armies involved, you could even miss each other completely and end up swapping provinces.

What does this mean in practice?

1) If we both have large armies and attack each other, is it 50/50 which province we fight in?
2) If he sends any army, even one unit to attack me, does he have a 50/50 chance of stopping my army moving?
3) If I break a siege, does that always occur before he moves away? Or could he in theory get away, start raiding other provinces and generally being a nuisance?

Thanks in advance for any light you can shed on this.

merlin