Diane and Henri lived in the 16th century, which was much different from today. Mistresses were the norm rather than the exception. In fact, Diane's husband was the grandson of the King by his mistress. Nevertheless, Diane was a devout Catholic, and she felt the conflict between her beliefs and her lifestyle very keenly.
You must also remember that Diane was a widow, a woman alone, who had to cope with the jealousy of the King's mistress. It was very natural for her to ask Henri for protection, and his infatuation since childhood had already turned to love.
No, she was no saint. I wonder why few people criticize her for continuing a liaison with Henry when it broke the heart of his wife, Catherine? This kind of behavior towards other women is hurtful and unconscionable - yet so many here honor Diane. Just a thought....
Aristocratic men and women were brought up with the idea that it was their responsibility to forge alliances that would enhance their families' prestige. Of course, one's proximity to the monarch was of prime importance not only for this reason, but for one's security. To have the protection of the king meant everything in an age when jealous nobles made
false accusations and claims in order to acquire another's property. We will never know how sincere Diane's love for Henri II was. But, she was certainly grateful for the relationship and her behavior, for the most part, was exemplary.
Of course, one must deplore her part in the Jarnac affair and her religious bigotry. Still, she stands along with Madame
de Pompadour as being one of the better royal mistresses of history.