What did MJ mean?

Well...

When u fall in 愛 あなた get butterflies. That person is all あなた think about. It's like being HIGH. it's the most wonderful feeling (like a high)

However... When you're in love, and that loved one theta hurt または hurts you, it hurts your very and あなた cry

That's the difference :)

i would say 'falling in love' is the start...u start falling in 愛 and then あなた are in 愛 and thats 'being in love'
maybe he means it makes him high to fall in 愛 but when he is in 愛 he cries? IDK! hahaha its just a song 'high' and 'cry' rhyme ...