Detaching and letting go doesn't mean stop loving. It means not getting sucked into the MLCer's drama. It means stepping out of their way and not impeding their journey. It's a protection for yourself.
Standing means loving unconditionally. Moving forward while leaving the door open a bit for a possible R down the road if/when S finds themselves and faces the issues that have caused them pain and then to run. They have to come to terms with the fact that whatever band aid they've used will not heal them and give them that elusive happiness they're chasing. Standing also means that you're giving yourself time to figure out what you really want.
Those gray or fuzzy areas that you find. Those are for you to come to terms with. Those are the things you will figure out as you take your own journey through this.
This journey that you're on, if you're open, will teach you that no matter how your sitch turns out, you'll be better than OK.