Hi Aimeth,
Depression is not only a side effect of chemo, it's a side effect of cancer.
Is your husband open to the idea of an antidepressant? If so, the sooner the better as it can take a few weeks before they help, if they are going to help. It's not a one-size fits all kind of thing, antidepressants, and sometimes folks get side effects, and when a person is taking many different treatments it's hard to pin down what drug is causing what symptom.
I have been there and done that. Had a rough time, too. But glad I started on Prozac about 2 months before my diagnosis (breast cancer, '99). I know it helped me through things I never imagined I could bear, and don't think I remember side effects being a problem. Then I switched to a newer drug, Effexor, and that one caused me huge problems both during and after using it. Worst of it was constipation and nightmares.
There's no easy fix. But it could be worth a shot. If possible, ask a psychiatrist to get on board, not just because they're medical doctors and know about interactions and things, but also because it wouldn't be a bad thing to have a therapy session or two along with starting an antidepressant.
If your husband doesn't want to go that route there is not much you can do aside from be there and love him. There is no wrong or right in this. It's a process he's going through and hopefully it will pass on its own, or come and go in phases. Depression and cancer is a huge problem that increases the difficulty of the situation for everyone concerned.
My heart goes out to you both. Good luck and I hope things get better.
Wendy