Either staying friends or detaching is about what you as the LBS can handle. They say the MLCer does remember how they were treated while in the tunnel.
I believe the problem with 'staying friends' is that there is a bigger chance for the MLCer to cake eat. That said, you know your H best. Would you be able to set and enforce boundaries for yourself that would prevent you from being used as a doormat? By this I mean that you don't want your H having the best of both worlds, you and the freedom to do whatever he wants.
Detaching is to protect you from the being whipped around on the roller coaster that your H is presently on. It gives you time to center yourself and to figure out what you want. It also gives your H time to miss you. It shows him what life is like without you in it.
Please remember that you didn't break him and you can't fix him. He has to face his inner issues himself. You can't hurry his journey up, but trying to interfere may slow it down.
This is not a fast trip your H is on. You have time to figure out how you want to handle this.
In the mean time GAL, work on yourself, and live your life for you. Do some of those things you didn't have time for before. Figure out who September is and what she wants.