Ending of the series *spoilers*
The ending is Denny is getting worse and gives all his stuff to Alan by being married to him. That was a way happier ending then I was expecting for the series.
I always assumed it would end with Alan killing Denny like he promised, and in turn Alan killing himself so they could be together. Then the last scene would Alan and Denny in hell, drinking and smoking and just talking about their situation.