Your young adult child is not just spending less time at home, but may be moving out permanently. While you grief over the "loss", the empty nest stage can be one of great personal growth and satisfaction.
This can be a time of rediscovering your own God-given purpose - without the kids. Seize the opportunity to try new things.
Your child is now officially on their own, when they learn what it means to be directly accountable to God. Your role is to support them in prayer, asking the Lord to bring to their mind the spiritual truths and moral principles you've instilled over the years.