my alpha is 46. i’ve known him for a little over 11 years. His sexual stamina is clearly winding down. He used to fuck me (in addition to his longtime gf) an average of 10 times a month now he only fucks me once or twice a month and its been going on for a year now. I now alphas are men of great power but do they go through manopause? 

Well, it may not be something silly like “manopause” and actually be something medically more significant. Sudden reduced sexual stamina or drive can be an indicator of disease or hormone imbalances. He should probably see a doctor.