This was something my father said quite frequently.
I only recently realized that I don't remember he ever actually said "I love you" to me. It was just so strongly implied that no one would dare question it. And the most frequent way it was implied was when I asked permission to do something, he refused it, I asked "Why?" and he replied:
"Because I hate you."
He said it in a sarcastic tone of voice, and it was meant to be interpreted as "What you want is bad for you and I love you, and that's why I won't let you do it." I think. That's how I interpreted it, anyway.
Now? Now it seems to me that even a pathological liar of his abilities could not bring himself to lie on this one. He told the truth for once.