It sounds like you're rather isolated and feeling lonely, which likely affects your depression. It can be very difficult to make friends when we are feeling low; but having no friends in the first place, can greatly impact our mental health.
I am also isolated, and recently have turned to online forums, like you. Perhaps through this platform, our sense of connection will improve, hence in turn, our mental health - other than that, have you tried trying to make friends in your area, perhaps through a community centre? A library can also be a good hub to seek out activities and meet people. Sometimes,the notice boards at shopping centres advertise Tai Chi or walking groups.
I also wonder, as you say you are married - do you have a close relationship and enjoy doing things with your wife?
Exercise does have a positive impact on mental health; but you mentioned you currently lack motivation. I can only say, that it takes three months to firm a habit - so the first three months WILL require determination on your part. Perhaps if you had a gym buddy, you could push each other to stay motivated- how about your wife?
Everything you say is reflective of the cyclic nature of depression- we want things to improve, but we lack the mindset to make any changes, hence nothing changes and we continue to feel depressed. I can relate to this, and I hope that through taking small steps, things will improve. Reaching out online IS a step you have taken, so this is great; you're hopeful and with that hope that things will improve, surely they will.