What happens if I attack an enemy but do not kill it? When an enemy has 3 health and I deal 1 damage, does it stay ready? If so do I need to spend another action (or two) to fight it again and again until it finally dies?
Also, If I fight and wound an enemy and then spend my remaining action points on something else, does the enemy do an attack of opportunity?
If you don't kill your enemy after an attack, the only thing that changes is the damage stacking on it. Defeat it or evade if you want to stop it from hurting you.
And since you have an enemy in your threat zone, yes, if you do something that's not Fight/Evade/Parley/Resign, you will take an Attack of Opportunity.