There's a proverb that goes something like this: A word is not a sparrow - once it gets out, you can't catch it.
Do you want your husband, or do you want a divorce? Because from we're he's at emotionally, if you say the "D" word to him, that's exactly what you are going to get. If you want you marriage back, talking about divorce is not the way to do it - it will not make him realize that his hurts are superficial and it will not make him run back to you.
Setting a hard timeline is also not how you do it. It took you 20 years to get into this mess. Do you think that a year's time frame is realistic? What happens if it's halfway better at the end of that year?
My advice to you is to do a 180, to get a life, and to think very carefully about what you want. Talk to a divorce lawyer. Talk to a financial planner. See how much this will run you. But do not discuss this matter with him and certainly do not give him an ultimatum. At least then you'll know that you tried and that you've made an informed decision.
Me: 28 H: 30 T: 9 M: 7
WAH: First half of 2017. Round 2 started in Spring 2018.