On forgiving

How do you forgive people who have betrayed you over & over again? People you have loved, helped and nurtured...how do you give them your trust again when they have destroyed that a number of times? Help me 'cause I don't know how. I want to but I'm afraid they'd do it again. I need to find a way to understand, to trust them again and to have that bond we once had. Help me. Please. My heart is open but my mind is not.