In order to best understand the concept of fatal degrees and how to apply them, what would be the best course of study?
Fatal degrees are simple. If the moon is in fatal degrees there is a chance the baby will die within a year so you need to look for things that maintain life as per the arishta bhanga yogas in the longevity course. Otherwise, planets that show disease that are in fatal degree give much more severe disease. But a good planet in a fatal degrees, nothing to worry about. Fatal degrees are meant to be used in teh rasi. I programmed t hem in the vargas to allow for research, but likely they work in rasi only.
Thanks Ernst that is clear and simple. Much appreciated.
If say Venus is debilitated in d1 and in fatal degree too, does it increase the chances of relationship being destroyed in its antardasha?
no, venus in fatal degree does not end a relationship, it hurts the health and longevity of the spouse. Fatal degree is very physical.