Rebuilding trust is not a unilateral process.
Both the betrayer and
the betrayed have roles to play.
The betrayer has to be extremely disclosing as well as consistent in doing what s/he says.
The betrayed has to give the betrayer a chance to prove his/her trustworthiness.
That means the betrayed needs to allow him/herself to be (safely) vulnerable so that the betrayer has an opportunity to earn trust.
If both parties play their parts, slowly and over time, trust can be increasingly reestablished.
_______