You raise a good point about a possible weakness in the virtue of forgiveness if—if—we appropriate that virtue exclusively without justice. When we forgive, as you say, we do sometimes delay exiting an untenable relationship as we stand in the hope of reconciliation. Even when we bring justice alongside forgiveness, we still may delay the inevitable because forgiveness does hold out that hope of reconciliation.
So, forgivers need to realize that the hope of reconciliation may not bring about a true reconciliation. Yet, as forgivers wait in hope, they have to keep asking the question, “Is the other capable of entering into a true, loving relationship?” If the studied conclusion is “no,” and if trusted confidants agree, then justice needs to come forward so that the forgiver is not left stranded for the rest of his or her life.
Yes, forgiveness may delay the conclusion that the other will never return, but a delay is not a permanent state. Eventually, a forgiver can and should stand in the truth of the other’s incapability of relationship (if this is true) and then act accordingly, but always in love and concern for the other.