Well, this is a very complex question...and a serious one.
Short answer 'yes' trust can be built up.
Not knowing why? it has been broken, is also hard to answer.
If it has been badly broken by something serious, then she must work out 3 things.
1.Does she love him still.
2.Does he love her still.
3.Is she willing to move forward, believing he will not do it again.(what ever it is).
If it is yes to those questions, it can be fixed.
Some people have had it happen, and have become even stronger than before...Because they were really in love.
Forgiving is part of life, and we all fall short in one way or another.
Some find out, others don't.
Finding out is a very good thing, now one has to ask''do I want to help mend this mess'.
Time as with anything, has to be your 'key-player' in this.
Once one has made the choice to stay with it, and learn to trust again...You can never ever bring it up again.(What the other has done).
It has to be put to death, never to raise it's ugly head again.
That is the hard part, forgiveness, has to be that.It must not be spoken about again.
That's where it is a 'grown ups' world. Success, is founded in strength.
From both parties.
The one who has done wrong can not be punished over and over, they will have to live with the memories for the rest of their lives, of what they did anyway.
We often think, ''oh they will forget''.They never do.It is impossible to forget.
So the one who has been wronged, in the big picture comes off better in a case like this.They do not have the guilt.
It is something the two of them need to sit down, and work out.No one else can really know, what they can do or want to do.
It is achievable,but hard work and lots of love for both, and time.
I actually would have a problem rebuilding trust in a relationship.
I don't think it is just a matter of time as I feel the hurt and betrayal would come back for me.
I think I would have to leave the relationship.
Maybe for some over time and with counseling.
I admire these couples.
For me the hurt and betrayal will prevent the healing process and I will be a resentful person.
It is best that I walk away form it.
The person who broke the trust need to ask for forgiveness and work at rebuilding what was lost by being open with their partner. talk things over. if it was cheating they should limit contact with opposite sex friends; Avoid leaving the room to take a call; keeping secrets such as with credit cards, business trips etc. Spend quality time with the person. Do not force forgiveness. If you are guilty give your partner time to work things out within themselves. If you are on the receiving end, do not hold the issue over your partner by bringing it up whenever the person does something wrong or expecting them to pander to you and be your doormat just because of wht they did.
Sounds like you have had some bad experiences donjo, but not all relationships are irreparable and sometimes both people in a partnership do want to make it work. I think you made a bit of a sweeping statement with this one.
You're the one who's 'sad'. Your pithy reply speaks volumes.
I believe, & deal in REALITY.
Life doesn't always smell like roses, although a person like you wants it to appear that way, so it makes YOU feel 'good'! It stinks, & reeks of c@&$ & BS!
Your fanciful thinking is the minimum, & at maximum, is gross stupidity. End of.