Your husband is experiencing hypogonadism. He should check his testosterone levels to confirm the stats and he should stop the medication/drugs or try to reverse the effects with estrogens patches. Hypogonadism may be “harmful” in patients with coronary problems and risky diabetes. If the fact is prejudicing his quality of life to the point where he cannot function properly in his daily routines or even cause it to be difficult any physical movement, then he should consult his team of doctors the soonest.
The next phase of his treatment with RT will add more side effects to the ones existing.
Some guys get them mild but in some they become nasty. Fatigue is the one more reported by survivors. It was also what affected me mostly but I managed to overcome the majority of the symptoms with a change in diet, habits and fitness program. Though I am younger (62) than your husband and I am retired.
Knowing about what I could expect after the treatments helped me a lot to overcome the effects. Try to educate about the matter by researching in the net. Type this in a search engine: “side effects from hormonal treatment and radiation for prostate cancer”.
Hope he finds a way to counter the effects.