MLC is just a label that is used for bad, selfish behavior. If you notice, we give pretty much the same advice to the walk away situations as we do the MLC situations.
What if it's not a MLC? Would you do anything differently? You've been w/him for a long time...was he always like he is now? If so, why now are you questioning his behavior? If he's not been this way his entire married life w/you, then there has to be something that's clicked to create the situation in his life. An internal crisis is like no other and it takes time to sort out...so what would you have done differently had this not come along?
You, and only you, can decide if your marriage is worth fighting for. You are the one that finally makes the decision as to whether it's worth saving and eventually reconciling into a new marriage. You will know when you've had enough...but it's not today or tomorrow or next week. How do I know that? Because you are still questioning what is going on and deep down, I know you are committed to fighting for your marriage w/your entire being. If and when the time comes to end it, you will be able to say that you've fought the battle and did everything you could to save the marriage. Until then...live your life as if today is the last day of your life.
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.