I realize you are very new to the world of MLC and walkaways and this forum, but please keep to one thread at a time. It makes it easier for us to follow your situation, as well as a good way to document what you are going through and you can refer back to your threads at a later time. You can change your subject line within a thread so that others will see it.
Now, I'll try to respond here, but will then go back and link this thread to your current one.
The first thing you to need to do is breathe! You have absolutely no control over what he's doing right now. Yes, he's running fast and furious because he thinks that your relationship was/is the problem. He's running because he wants to end the relationship w/you because he thinks the grass is greener over on the other side of the fence.
If you are going to have a discussion w/him, be prepared that if you give him an ultimatum, he will choose the easiest route and that would be w/the ow. If you are absolutely certain that you are ready to end your marriage, then move forward. Right now, he's in his own little selfish, self absorbed world of "me, me, me". Let me just say this, if his life was all happy and fun, he wouldn't have to tell you. A lot of times, they tell us this stuff so that we become miserable and unhappy, but I can assure you, once the euphoria wears off, the routine settles in, etc., he's going to find that life isn't a bowl full of wonderful, sweet cherries.
Actually talking to him won't do a bit of good because conversations go in one ear and out of the other. The best way to get them to "hear" you is by actions. Actions always speak louder than words. If you threaten divorce, you better be ready to file because if you don't, he'll know you are bluffing.
Bottom line, you have to protect your assets and take care of yourself and your children. If filing means that you are going for child and spousal support because he's not paying, etc., then you will need to do so. There's nothing wrong w/filing when it comes to support issues. Watch your accounts, document any and all spending he does, if it's coming out of joint accounts.
The advice that we provide here for MLCers and walkaways will be the same, leave them alone, no relationship talks, focus on you and your children, protect your assets and finances, etc. and learn to live your life as if he may never return. Bottom line, you need to decide what is best for you. If you are ready to file, then file...you don't need to advise him unless you are hoping to change his mind...btw, it won't because you will be doing the dirty work for him.
It's your call as to what you want to do...but actions do speak louder than words.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.