Please get yourself to a clinical psychologist trained in CBT as soon as possible. Call and book an appointment by the end of the week. Ask them for books to read after.
What is CBT?
Exercise really helped me when I was depressed. I took SSRIs for 2 months and didn't like them so stopped. But joining a gym with my husband and going together got me back to normal. You said you are both unfit could you phrase it that you would like to get fit and need his help. He might be more receptive if it's not focused on him. Obviously doesn't have to be a gym could be early morning walks/runs.
I should clarify. We're not in shape for running around for 1hr 20m with a soccer ball (as noted above, it's hard to find females on the co-ed teams, so that means running hard the entire game, no breaks). I'm actually at a 21-22 BMI, solidly in the healthy range. (Been working on improving my diet over the past 2 months, cutting out coke at lunch and finding healthier receipes for home, so I've lost about 8 lbs, which at my height/weight is not inconsiderable.) His BMI puts him in the overweight category, at 26-27. He enjoys walks, so I've been trying to suggest them more often. About 4x a week we walk from work to the train station, and sometimes the reverse too in the mornings, from train to work, which is 0.7 of a mile each way, rather than take public transit. Also have done a few walks around a pond near us (1-3miles, depending on how far we go), although we really should go more often than ~1x per week. Maybe I can get him to make it a regular thing a few times a week. I'll also have to look into diet modifications and see what I can do there. And see if I can find a regular activity for us to do together. It's a bit tricky because I feel I'm reaching the capacity of what I can join right now, until I scale back on my volunteer work, which won't happen for 1.5 years (I'm President of the Board), but I'll squeeze it in.
Last night seemed to be improved. We saw a movie (free screener tickets), and talked on on the mile walk home. He also did say that he loves me very much, he knows it's hard on me, and he doesn't know what he'd do if his unhappiness (he doesn't call it depression) pushes me away and he lost me, because I'm the only thing good in his life right now (no pressure there...). So I don't thinking issuing an ultimatum is the right approach, I think it'd spiral him down. (Argule, just saw your post after writing the above. Maybe it depends how I frame it and approach it.) He talked to a friend whose been trying to reach him (but he hasn't wanted to talk to him because he didn't think the friend would respond productively to work complaints, so I suggested he not engage over work conversation and talk instead about other things, which he did). Also talked to his mom who is back from France. And, this morning he told me he thinks he may take a mental health day tomorrow, his first ever in his life - which I'm going to optimistically see as a sign that maybe he will finally consider other changes as well.
In regards to how long this has been going on question, well, he's always been a pessimistic person, though he'd call it a realist instead. When we first started dating 6 years ago (2008), he wasn't thrilled at his job, but it wasn't quite like this. After about a year or two, he started to get unhappier there because of his boss, so I encouraged him to look elsewhere. He didn't really interview much, just at the current place. The current job is a tough one, I will definitely grant him, without much support from the company. He had an effective boss initially, but then switched bosses about a year ago which definitely helped. Unfortunately, issues such as understaffing for their model (compared to peer organizations) are excerbated by one person being let go, a person out on maternity leave, etc. on a very small team. Last Oct they knew they needed to staff up, and got permission to make 2 hires, but are in the same place as then, with no signs it'll improve soon. His job also involves a lot of rejection - telling other people no. He's also frustrated at his inability to do things for his people (e.g. getting a bonus or recognition for the person covering the job where the person was let go). So it's gotten worse and more problematic over the past ~3 years. He'll have waves where he thinks it's getting better (though never well), times when it putters along not great, and times when it's definitely worse. Progressively more down time as it goes on. I once likened it to an abusive relationship (when he was in an up period), and I think he agreed.
In regards to kids, yes, I want them, I'm not on the fence. I thought we had agreed to have them in fact, before I agreed to move in with him and get married. I found out later he had a different interpretation of our conversations. His concerns re kids used to be financial, whether we could afford them. (It does not help that my sister is queen of kid-consumption with over the top things like birthdays and christmas.) As you all well know, kids don't need to be that expensive. I think he is more ok on the finances now, but recognizes this decision would prevent him from retiring early (so he thinks, particularly as he feels obligation to pay fully for college), and that coupled with his job hatred, is problematic. Of late, his concerns have been more that he'll have no energy for them, leave me with all of the work, and I'll get extremely frustrated by it. My nephew is pretty high energy and when we we see them, we're the "exciting toys" he wants to play with, which also probably doesn't help. I have my annual appointment with my doctor at the end of July, so I'm thinking of trying to get him to come with me and hear what the doctor has to say regarding timing/fertility.
