Besides its monthly cycle, the moon changes daily. Sometimes it looks like it rises in the east. Sometimes it looks like it rises in the west. Some days it is red or blue; some days it is so dark it can barely be seen; other times it is so big and orange it takes a person's breath away.
I'd say none of us worry that it won't be full again or that it has vanished when we can't see it. We know it's there. We don't worry about it. We know it is a constant that God has placed in the sky.
We trust God to bring the moon through all her cycles and phases.
This kind of trust is the kind of trust we need to have when it comes to those we love. I see people I love struggling to have faith or struggling to trust God or struggling just to live. And I pray for them. But when I start thinking about them, I sometimes begin to worry. I forget that most of the work God does is under the surface where we can't see.
God is working in the unseen realm. He is coaxing your loved one's heart to open to His grace. He knows so much more than ever could know how to reach that individual.
Trust Him with your loved one. Trust that even if that loved one seems to emotionally disappear or explode that God is at work in your loved one's heart and life. God orchestrates situations to reveal Himself to people.
Keep trusting Him with those you love most of all.
"The prayer of a person living right with God is something powerful to be reckoned with." James 5:16c