I totally sympathise, both as having lived with someone with severe depression and also having suffered several severe bouts myself.
The problem is that the illness saps one of energy, persistence and motivation which are exactly what is required to seek help and stay the course.
Sertraline worked for a while but am not on anything now. Good, quality, food for energy and nutrition are essential. Fresh air and country walking really help. A regular sleep routine as does anything that soothes and comforts, except alcohol. A regular daily routine helps me too.
I have seen a number of counsellors and therapists over the years and they have ranged from downright dangerous to ineffectual to absolutely life changing. Avoid anything AI based. It's a joke. Long term psychotherapy worked best and the lady I saw for several years was absolutely fabulous. She has now retired and moved away sadly.
He will need to try a few to see who fits best. Always ask about qualifications and what type of therapy they practice. You have to like the therapist or counsellor, I have found, and also it helps if you're of a similar educational background. Mutual points of reference really help. What works for some doesn't work for others. I found CBT a waste of time and that tinkly music that is supposed to 'balance the brain' infuriating, but others may find it helpful. I needed someone with empathy but who would also recognise when I was starting to wallow, and point this out.
My heart goes out to both of you. Trying to help someone who is in a pit of despair is really hard. I found even walking into the same room as my ex sapped my energy somehow. It was like the space was filled with a suffocating grey fog. I felt so helpless. That's why it's important to maintain your own interests and routine.
He is facing losing his job and the sexual dysfunction too must be very distressing. Suggest he looks around at the therapists available to you locally and encourage him also to persist with the medication for now - but it doesn't always help everyone and can initially make things feel worse.
Exercise does not need to be a full on gym routine. He is ill. Gentle walks and just doing one small constructive thing each day might be a good start.
All the best to both of you.