Usual disclaimer, usual references (for me at least.) Enjoy, but if you don't like, don't read. If you've burn't your eyes out by the end, don't blame me - you read on.
Guilty
He was guilty of being unfaithful.
He was guilty of lying.
He was guilty of lying to his first lover.
He was guilty of lying to his second lover.
He was guilty of lying to his third lover.
He was guilty of lying to Sirius, saying that he was over him. The truth was, Azkaban broke him. He could not stay and love a broken man. There's only room for one with emotional baggage in a relationship, right?
He was guilty of lying to Harry, saying that it was wrong. Wrong that he was taking advantage of his dead best friends' son, his former student! Though they still took every opportunity they could to make love, even after he said no more.
He was guilty of lying to Nymphadora. He said he didn't love her. He said he was too old, too poor, too dangerous, the truth to a point. But he didn't want to pull her into his shit. He was still in love with Sirius, long after he had died. He kept fucking Harry. Hell, when he tried to run for Dora and his unborn child, he found Harry, who was only too happy to greet him with a welcome-back fuck.
Can you see now why he was guilty?