You've got a tough row to hoe on this one. It sounds like she might have a clinical depression, which can be treated if she goes to the doctor and asks. I would ask her to get an evaluation.
You're at the end of your rope - that's clear. Blindside her? You don't need to do that. Since you're already on the verge of leaving, you may as well put all your cards out on the table and give her a chance to understand where you're coming from and see if she wants to make it work. I don't mean that you should be cruel to her, but be honest with statements like these:
Our lifestyles don't match - I want a partner who will join me in things other than children and home address.
I'm unhappy with your energy level and your daily activities. I'm finding it harder to respect you and your choices.
When you continue to gain weight, I feel pushed away.
When you continue to be attached to your failing business to the point that you'll lie to me about it, I feel hopeless and unconnected and angry.
I'd like to sit down with you and find out where you're at on these issues and see if we have something to work towards together in our marriage. If not, I'm going to accept the truth of what it has become, which is something I'm no longer able to be in.
I'm willing to go to counseling, but only if working on our marriage becomes our #1 concern as shown by a change in behavior. This isn't a joke, it isn't a threat. I'm telling you that I'm on my last leg and feeling hopeless. I'd like to make this work - will you join me in that?
I think if you use statements like those, you'll have something to work with.
My best to you,
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