I don't think this is necassarily a matter of wanting to get better or trying hard enough to get better. That's not how clinical depression works. You can't just "snap out of it" and no amount of forced smiling can make it better.
There is a lot of stigma with depression in that the person suffering has a level of control over how they feel. And in some situations, people do - they can get out, try to interact more socially, etc. After a certain amount of time, however, when that doesn't seem to be effective or when people are struggling to find the motivation to even try to do something for themselves to help their mood - you're looking at something much more serious. Another indication that you may need more than self-help is when relationships become strained as a result of the depression.
Depression (particularly clinical depression) is better thought of like a medical illness, like type 1 diabetes. People are born with this disease and they need intervention from medical professionals to guide them on how to live their life with this condition. No one would choose to have this lifelong disease - and no one would choose to feel depressed and put a strain on their marriage and other relationships. This is not your fault. You are not choosing this - no one does. A good place to reference about this topic further is the Self-Help section on this site titled "Depression".
Your wife, like most people, doesn't understand the complexities of this illness. This lack of understanding is making it difficult for her to support you in the way that you need as you go through this. This isn't a one sided situation where you have to do all the work and she's just waiting for you to get better. If you do have clinical depression (which, again, only a professional can determine) it can be a lifelong disease andhave ups and downs. Sometimes people get brief intervention and things are okay from there on, and sometimes it's an ongoing process. Again, just like a medical illness. You may try to control a medical illness through exercise and diet, but you can still have "flare ups" from time to time that need intervention from a medical professional.
What's concerning to me now, is the lack of support you seem to have at the moment. And we're always here at 7 cups to support you emotionally by being good sounding boards and listeners. I also think it's worth a shot to talk to a professional about this, so you can develop a plan of action together, talk to your wife about the expectations of your treatment plan, and what you need from her to get through this together.
I'm sorry you are having a difficult time with depression, and I hope you're able to get help and work together with your wife to get through this.