When we deal with people we know we can trust, we know that we have someone that we can confide in with any given secret in our lives, and know that it will not ever be leaked. Trust is one of the biggest relationship makers and breakers, because with trust a relationship is able to grow, and without trust a relationship will crumble.
When we decide to trust someone after they were dishonest or disloyal to us the first time around, we are choosing to put our heart into someone's hands with whom we know is capable of hurting us again. With this being said, knowing that they may be able to hurt you again is not what should be focused on. Instead after a thorough reconciliation and grieving period we have to be willing to get past the past in order to grow the relationship.
Being in a relationship with someone who has already hurt you may be harder for some, and easier for some, depending upon their tolerance for pain, and how forgiving of a heart they have, but make no mistake about it, it will definitely be an uphill battle. Just remember that your heart is special, and if someone wants to be in your life after hurting you once before then they need to earn this spot back into your life.