Sure, Jane Thor is in the comics. Her character brought a fresh perspective and showed that anyone could be worthy of the Thor's power and responsibility.
Love is a very common theme. Their relationship, whether it's the budding of their love or the challenges they face as a couple. Another theme is adventure, as they often go on quests together. And power, like how Thor's godly powers interact with Jane's scientific knowledge.
Love is a very common theme. Since their relationship is central in the movies, fanfictions often expand on their love story, exploring how it deepens and overcomes obstacles.