I'm sure the answer is never, but is there ever a right time to explain this to her?
I tried reading your post a few times but I'm still not clear on what you want to communicate to your W, is it that you may be in depression? In the end it's up to you what you want to share with her, but just don't expect it to change your situation. A lot of LBS's pour their hearts out to the WAS after BD to try and show her they can be the sharing, sensitive husband that she felt like she didn't have, but the problem with that is the WAS is really quite done after BD and really doesn't care to hear it all. They usually think "too little too late" and may even think "wow when did he become so pathetic and needy." That said, something like clinical depression is a serious health issue and personally I don't think it hurts to let those around you know about it, including your WAS. As long as you share it with her on an informational basis, not with the hopes of bringing her back. Does that make sense?