How do you define this word?
Generally speaking, I would define love as a strong positive emotion of regard and affection but the determinant is, the context in which it is being used.
When someone says to you ’ I love you ’....does this phrase ( I love you) prove his love is true?
Not necessarily. Even though the words may be conveyed in the most convincing way possible, the proof is in the actions portrayed by the said individual. People have always figured a way to manipulate the use of the words " I love you" but their actions eventually expose their heart, true feelings or intentions.
How do you know if someone loves you?
This boils down to how they treat you; how sensitive they are to your needs/concerns, their willingness to care, forge a relationship despite the odds, compromise, commit,......etc.
Is love nothing but some simple words we say to each other?
Love is far more than just simple words uttered.........its comprehension, way beyond our imagination but somehow, it is typically reflected in our actions towards our self and each other.