I know first hand about the freakin craziness of all this. I hate the term mlc. Honestly I feel a crisis is a crisis at any age. My wife seems to be way too young for this too, but she fits it to the T. I believe something happens in childhood that causes them to not fully develop emotionally. Later in life a trigger occurs that forces them to go back in time if you will.
You have to understand that if he is having a crisis he didn't ask for it and has no idea what is going on inside of him right now. They all blame the spouse and focus on us as the problem. That is the name of this twisted game.
There are no quick fixes and really nothing you can do but love him from a distance. The "other person" is a symptom not the problem. Many of them turn to someone else and believe me the person they turn to is usually broken in some way as well. They can never have a real relationship together.
Time and patience like never before is the only way this comes to an end. It is an extremely bumpy road. Depression is what fuels this crazy behavior.
Regardless of what you decide, you have children together so you will always have that connection. You really should take the time to get educated about what is happening to him. I'll give you a link with some very good info.
Only you can decide when enough is enough. You do need to protect and focus on yourself right now. There isn't much you can say or do. The more he puts his focus on you as the problem the longer it will take. So detaching and distancing is very important for your sanity and his crisis.
Please check out the stuff on this link to give you a better understanding of what is going on and remember believe none of what they say and only half of what they do. Learn about what is happening and ask questions.