Opposites (Fairy tail)

He was a male, she was a female.  She was left-handed, he was right-handed.  He was popular, she was the nerd.  She was clever, he was dumb.  He preferred warmth while she loved the freezing cold.  He was overly confident, she was extremely shy.  She was bad ass, he was ordinary.  He had a bright personality, she had a dark one.  She was a loner, he was always surrounded by people.  He never took things seriously, she was always serious.  Her family was dead, his was alive. He was someone, she was no-one.  She was demon, he was an angel.   

Then how could he fall in love with the demon while he was an angel?