Letting Go doesn't mean you don't love them anymore. Letting Go doesn't mean you won't miss them anymore. You'll always remember. You can never cut the ties that bind two souls together who truly love each other. What you DO need to cut is the Leash of Grief and Guilt that binds them to you and prevents them from doing what is best for them.
As They say, set something free and if it was yours to begin with, it will come back. It's natural law, in Heaven and on Earth and in all the spaces in between life and death and life. Your loved ones cannot come back from a place they have not yet arrived.
If you are looking for Signs and not finding them, take a look at what you are doing. If your best friend is still on the leash of your grief, your best friend is not yet free to be everything he or she can be.
Letting Go is the most important thing you can do for both of you. It is the ultimate act of faith... and you will be rewarded for it.
Breathe. Then Let Go. It's time.
You say you love. Do you love them enough to let them go?
Do you trust them enough to have the faith that they will never leave?
"'Do not cling to me,' said Jesus, 'for I have not yet ascended to the Father.'"
(Jesus to Mary Magdalene)