The three musketeers

STORY
This is the story of d'Artagnan and three musketeers Porthos, Athos and Aramis. They fight bravely for their country France and for the king.

Well, I was shocked a little to read this story because I couldn't see that d'Artagnan is a righteous person. Maybe, he is not a bad man but I think he is a simple and very stupid person.
When his girlfriend Constance (actually, she's married but she loves d'Artagnan.) was kidnapped, he tried to help her out, but he met a beautiful Milady and fell in love with her! Then he completely forgot about Constance (what a man!) and tried to be close with Milady! He tricked Milady to love him. He lied to her but it turned out (actually, he confessed by himself. He is really stupid). Then, Milady got very angry for d'Artagnan's lie and tries to kill him.
Don't you think it is natural because d'Artagnan is wrong? I think it's all his fault.