Get a lawyer, get an order for temporary support, DO NOt make any agreements with him about finances until you have legal representation and advice.
Yes, it sounds like he's going through a midlife crisis but there's no guarantee he ll come out the other side or when he will. If he feels you clinging he'll be even less inclined to come back. Get up on your feet and start living your life AS IF he's not coming back and you are pursuing your dreams. It doesn't mean he won't come back - but he's more likely to if he sees you out living your best life without him. If he thinks you are just waiting around as his PLan B he won't feel your loss - and he needs to feel that.
And - just one question - a big red flag - why on earth did you marry him after only 3 months of dating? Are there any clues there? Most rational people are not that impulsive - but love addicts go for that, and sociopaths may love bomb people like that. I'm not saying there's anything wrong BUT I also wouldn't be surprised if, as time goes on, you start to realize that your rosy perception of him during your marriage may have been glossing over some serious issues.
