This is an image currently doing the rounds on Facebook. It's supposed to be a cuddly-wuddly warm fuzzy, I think. Well, it should creep you right out.
Human beings are not perfect creatures, no, and some are more flawed than others. Indeed those we love the most are often full of flaws, just as we are ourselves.
However, making excuses for behaving badly, and justifying it by saying "but I love you" is not right. Let's actually examine what this really says.
It says "You MUST forgive me. I demand it. Even though I knowingly and repeatedly treat you badly, and fully expect to do so in future, I demand that you put up with this."
This is the behaviour of what we have come to know as the "vampire". They don't suck blood. They suck your attention, your time, and your good nature. They use subtle forms of emotional blackmail to keep relationships going, because they are selfish, self-absorbed, and irresponsible. But they put a smiley face on it, dress it up as love, and expect everyone to go along with this scam.
Almost everyone has had one of these social leeches at some point in their lives. Due to our upbringings, we have fed these vampires, and you only have to feed them once for them to latch on.
It happens because we want to be nice. We want to be kind, compassionate, caring, and above all polite. Vampires take advantage of us, and if we tire of their bad behaviour, and try to ease them off, they try harder to stay attached. "But I've been a loyal friend! Why would you push me away?"
Some of them are so very subtle that it takes us time to recognize what's happening. Studies have been done, however, and much has been written on the topic. You can find plenty on Google if you suspect you have this type of person in your life, but here's a good read: http://friendship.about.com/od/Friendship_Definitions/g/Emotional-Vampire.htm
Once you realise how these folk operate, it all becomes clear very quickly. You'll soon spot them a mile off. You'll recognize the rinse and repeat cycle of insults and apologies. All you need to fend off vampires is discernment. No garlic necessary.