I know it's hard. Seeing them like this. I know it's killing you and all you want to do is take their pain. But I need you to remember something; it is not your fault and you cannot fix it. You can be there for them to cry on, when they need to be listened to, when they need an ice cream run at 3am. But you have to realize that as much as you want to, you cannot fully understand what they are going through.
Please remember that when they isolate themselves or ignore you, it is not intentional and it's not anything you did. At this moment they have a million thoughts racing through their mind and can only handle so much at a time. It's not you. They're trying to process and understand.
Helpful suggestions and honesty are great things, but timing is everything. If they just want you to listen, listen. Cry with them, hold them. If they ask for your advice, give what you can. Just keep in mind that sometimes their heart is already so overwhelmed that they can't process any more.
If they are isolating themselves or sleeping a lot, let them. They are emotionally exhausted from fighting and need time to rejuvenate. Yes, eventually they will have to get back into society. However, in the stage they are in they can't handle a lot of people, nor do they want to. Let them hurt, and let them rest. They've needed to for a long time.
Let them know it's okay to not be okay. All they've ever learned from society is how to put on a mask to make others feel comfortable or strong. In these crucial moments where they feel weak, where they are crashing, they need to know that they are allowed to hurt. That they don't have to be strong for anyone, not even themselves. Being told over and over again that they had to pretend in order to be okay got them believing just that. So maybe if we slowly and gently push the idea that being real actually helped them heal, it would reset their whole mindset.
Take it slow. Recovery is never easy and sometimes in order to heal they will have to do things that are out of their comfort zone. But don't force it. Remember that small steps in your eyes may be big steps in theirs. Respect the stages of their process.
They don't need you to be strong for them. They don't need you to put on a happy face if you're hurting too. They just want you to listen, to be respectful of their pain. To be there when all they want to do is give up. All you have to do is be. Just show up and love them and you've already done the best you can. They will be okay. But for now, let them hurt. Healing takes time and they have to heal in order to rebuild.