James is portrayed as whiny and not as brave as his teammate Jessie, but he has a very gentle and nice side to him, and will get things done when he puts his head to it. Growing up in a rich family and having people heed to his every beck and call, it seems as though James hasn't fully developed a strong backbone for himself and thus needs someone to depend on or to work for. It’s evident that Jessie is this person in the episode of "Training Daze", as he makes a promise to her several times that he will never let her down.
The young man cares for Jessie and hates when he sees her down. In "Princess Versus Princess" Jessie has her heart set on winning a doll set. When it seems like Jessie is about to lose, James is obviously upset for her, as he falls to his knees and exclaims "Jessie can't lose!" After her defeat, James even cheers her up by dressing himself, Meowth and their Pokémon as a real doll set.
James has proved himself to her and is willing to please her. In "The Ultimate Test", after Jessie is expelled (or rather, after she leaves in the middle of an exam) he devotes himself to her by saying "Jessie's been expelled. Now I have to do my best for her!" and when battling the exam man says "This one's for you Jessie!". Her love for beautiful and cute Pokémon causes the entire team to often go out of their way to try to capture them. But James is always willing to give an extra hand. In "Beauty is Skin Deep" James immediately obeys Jessie's call to catch the legendary Dratini, as he sends out his Weezing.
He has proven his need to be with Jessie. In "The Ghost at Maiden's Peak" after being aware that he was possessed by the ghost maiden, James was incredibly scared - Unlike Brock who was very willing to be taken away by the maiden. He was also very upset after he was told by Jessie that the anti-ghost stickers were free and made it very clear that he didn't want to go with the maiden; "I can't believe you're letting that ghost get me just because you're both so cheap!". But he was very content with the fact that Jessie "really [did] care" for him after she shot down the maiden.
In "Holy Matrimony", his devotion to her and the team is proven further. James was supposed to be married to Jessiebelle, but returned to Team Rocket despite the fact that he could be rich again. He would rather be pinching his pennies with Jessie than stuck with Jessiebelle and his family. Although Jessie is very selfish sometimes, James always finds it in himself to forgive and forget, as shown in "Bad to the Bone". Jessie had run off with the badges that the three had stolen to enter herself in the Pokémon League. After James and Meowth had found her, James reunited himself with her by simply reciting their Team Rocket motto.
James cares deeply for Jessie and she seems to be the support he needs – To the point that he has given up a rich and lavish life just to be with her and Team Rocket.