Forgiveness

What's harder? Forgiving someone who constantly lets you down? Or forgiving someone who let you down once, real badly? I'm not sure of what I'm trying to get at.. but I just need to vent at the moment. Someone told me that the reason it's so hard for me to forgive someone who let me down real hard is because I used to care about that person the most (and our relationship was real) that when they let me down, I was too disappointed to want to give them another chance. Someone else argues that the reason I can't forgive that person is because I STILL care, and I just can't get over the pain. I honestly don't know. Maybe it's both. I just know that right now, I'm not really up for forgiving.. And as for people who constantly let me down, why is so much easier to forgive them? You'd think it'd be more frustrating to have to keep forgiving someone almost on a daily basis.. & To be honest it's really really ANNOYING to feel so unsure about someone just because they only talk to you when THEY want to. And yet, I still find myself forgiving their inconsistency day after day. I admit some days it really pisses me off. I don't know why I can forgive them though, and not the other. I just don't understand what or who inside me makes the decision of who to forgive.. or why 'it' chooses to forgive one and not the other. They say forgiveness is the key to a happy relationship: accepting that we are all human and that we all make mistakes.. but I don't know. What's worse, a relationship that's so safe it feels unreal, or a lack of a relationship because it was once oh so real? You know, it's like the whole "it's better to have loved and lost than to not have loved at all." Is that really true? Does pain really constitute how real something is? Or was? I don't know anymore.