Maybe letting a loved one go -which to any of us who love another, can seem scary in a way...is based on our sense of 'time' here on Earth?
Where there's real love between two Souls, that love can't die, or dsappear. It can evolve, change shape, but it isn't going to die if it's true.
We're on Earth to experience a whole range of things. It's not a pain free experience. It's not without soul-yearning and a feeling of maybe not quite being in the 'right' place with the 'right' Souls.
That's a worm's-eye view though. We are never truly separated from genuine loved ones where the love is mutual. From the vantage-point of spirit, even our lifetime is like one day.
But 'letting them go' is just like letting them go free without imposed restrictions, to have their own experiences. Very often, we find, (sometimes even to our amusement, in Spirit!) that there never ever really WAS a separation. All our loved one needed was to go exploring for a bit, and have individual life experiences. And that we needed those things too.
Outside of the concept of Earth time, things can look very different.