2006 dodge durango. I had a valve spring break. Now they are saying that the valve isnt sitting right. I know that means its not sealing correct, or something in that general manner. what else should I look for or watch for? My thinking is that the head might have to be replaced. Any opinions? And, why do valve springs break in the first place?

metal fatigue
simple defect in the metal.
If the spring broke, it'* quite possible you had PTV which caused you to bend the valve. You can simply have the head inspected to see if the valve guide cracked. I'd also check the piston for the cylinder with the broken spring and see how much damage was done. Just my .02