Please do not double post. We have an edit button on the bottom right that allows you to update your post.

As for the fleeing, there is no flee button available in the game that is specifically labeled as flee (as it is traditionally known in RPGs and FF). The way you flee is by pressing the start button and then pressing the select button to retry, which will remove you from battle and place you a few seconds prior to your engagement of the enemy. This way you can avoid the fight if you wish or take another attempt at it.

As for the final boss in the game. It is only about the Crystarium up to a certain point. So long as you are fighting the majority of the monsters you come across you will be a fine a position to fight, because the battle is more about strategy than it is about having a lot of strength or HP. Strength will certainly get you through the fight faster, but in the end a good strategy will help more than grinding CP. Sadly, the death ability he has is a pretty cheap shot and I've always thought that. The death card is about the only thing that is something you can't really avoid unless you have an accessory that improves your resistance to it, which one can be found in the final dungeon. But you can win without it, since his death I'm pretty sure has the same chance of succeeding as yours does, it just doesn't really feel like it sometimes.