ENOUGH TIME + THE RIGHT STUFF = TRUST
It's not uncommon for people (especially the unfaithful partner) to expect a quick return to trust once "I'm sorry" has been expressed. It doesn't happen that way. Real trust will only be experienced when these 2 ingredients have been appropriately mixed:
What is "enough" is different for each couple and situation. Most relationships, however, require at least months before trust can be genuinely felt. A person may choose to act in trust until it is fully earned, but you can't short-change time for the real work of trust to be completed.
The Right Stuff
Time itself isn't enough. The time has to be filled with the kind of behavior that provides assurance to the betrayed spouse that they are safe again.
You have to have both! Either ingredient by itself (time not filled with trust-earning behavior, or the right behavior for just a little while) is not enough.