A Riddle

What is sweet at first but bitter after,
It can turn a whole room bright but it would still be dark sooner or later,
What is beautiful on the outside but ugly on the inside,
It changes it looks as well as you but you'd still be yourself,
What lies and hurts you the most,
It brings you nothing but tears and anger,
What we need most in life but somehow manages to take away life itself,
If you still don't know it is,
It is what we called love.