He is a ruthless and somewhat naive and is madly in love with Jeanne as he would do anything for her, from lying about being part royalty to get more money, to attacking Rosalie when Jeanne told him that Rosalie would expose her sister as a peasant so he can protect her future and her dreams of living a luxurious life, even going as far as killing the woman who helped Jeanne become a noble lady so she can get her fortune.
When Jeanne became unhappy with their lifestyle and not having more money, she conspired a plan with her husband to get the diamond necklace being made for Madame du Barry and frame Marie Antoinette when she wouldn't give the couple anymore money.
When Jeanne escapes prison, they intended to kill Oscar Jarjayes but it backfires as Jeanne was shot and was dying. Nicholas was devastated ad cries to Jeanne that he doesn't want to lose her, making Jeanne realize that he, besides her sister Rosalie, was the only one who truly loved her and stood by her. Not wanting to die alone and saw that Nicholas doesn't want to live without her, as well as realizing that her husband would be in prison and sentenced to death if caught, she stabs him so they could die together, before the building explodes, Jeanne apologizes to Nicholas saying she didn't want to die alone, but Nicholas happily says that wherever she goes he will follow her, then the two share a passionate kiss and they die in the explosion.