Instead of telling him that you want your marriage to work, try something similar to "I know I am going to have a great life. I would love for you to be a part of my life, but if you choose not to, that will be your decision"
Sara, Lots of good advice here. I particularly like what MC said as I said something similar to my H. I told him I, and our D14, would be fine. It definitely registered with him. I made sure I had mentally rehearsed for it. I was calm, strong and confident when I said it.
Also, remember the 48 hr rule. It's always good to think about things before acting ... but you probably feel you've already been doing that for the last few weeks.
You know you have a lot of people praying for you here.