Easier said than done, but it may be better to continue to value each other, as good people, who just don't quite make the right fit, so you need to move on, and hope the other person does meet the right person.
In terms of not letting go, I think you need to see yourself as something of value. You are important too! Your needs are important too, and this needs to be taken into account, when the letting go monster turns up.
RE: Letting Go