Our natural inclination is to excuse these behaviors because of the illness. This is very easy in short-term illnesses where the diagnosis is straightforward and simple for others to understand. However, when there is trouble getting a diagnosis, or when the diagnosis is difficult to understand, or when the disease seems unending, the behaviors of the sick person can seem unacceptable. Relationships that are already weak are the most vulnerable to the strains an illness produces. When partners lack communication skills, or don't use them, when they are quick to accuse and slow to forgive, then illness can cause a crippling blow.
Endometriosis is a disease of women.
This question implies that men should understand your pain and disease. Let's agree that they should try to understand. As noted, the entire menstrual cycle is foreign to a man's experience, and endometriosis can be totally confusing. If men are involved in the entire process of evaluating the problem and seeking a correct diagnosis, they tend to reach a greater level of understanding. Therefore we in the medical profession need to encourage men to be a co-student in the learning process.