Their relationship can be developed through shared experiences. For example, they could face a common enemy together. This would force them to rely on each other and understand each other's strengths and weaknesses.
In fact, their relationship wasn't really a 'love story' in the romantic sense. What made it special was Carlisle's role as a protector and a moral compass. He was always there to guide Bella and keep her safe. His wisdom as an old vampire was something that Bella could look up to. He added a sense of stability to her life in the chaotic world of vampires and werewolves.
Well, Carlisle is a very different kind of vampire. He has a sense of honor and ethics. In relation to Bella, his connection was mainly through Edward. But Carlisle was always there to support Bella, to make sure she was okay in their dangerous vampire world. He was like a guiding light for her, not a romantic partner. Their relationship was built on his respect for her humanity and her place in Edward's life.
One common theme is the exploration of a forbidden relationship. Since Carlisle is much older and in a different position in the vampire hierarchy compared to Bella, it creates an interesting dynamic. Another theme is the idea of mentorship. Carlisle often acts as a mentor figure to Bella, guiding her through the vampire world.
You can start by looking on Fanfiction.net. It has a large collection of Twilight - related fanfictions, including many that focus on Bella and Carlisle. Archive of Our Own (AO3) is also a great place. It has a wide variety of fan - created works, and you can easily search for specific pairings like Bella Swan and Carlisle Cullen.
In some fanfiction, their relationship develops quickly. They might share a moment of intense eye contact and instantly feel a deep connection. From there, they start spending all their time together, getting to know each other's likes and dislikes.
In fanfiction, their relationship might develop through a series of adventures. Suppose they go on a quest to find a rare artifact that has the power to either save or destroy the vampire world. Along the way, they face numerous challenges like dangerous terrains and other powerful vampires. During these hardships, they start to care for each other more. Peter might show his protective side towards Bella, and Bella might be the one to give Peter hope and a new perspective on life. This would strengthen their bond.
Fanfiction.net is a really popular platform for 'bella swan and carlisle cullen fanfic'. It has a large collection of stories, ranging from different genres and writing styles. You can easily search for specific tags related to bella and carlisle to find the fanfics you're interested in.
Another fanfic could be 'The Unforeseen Alliance'. In this, bella and carlisle find themselves in a situation where they have to team up against a common enemy. It's full of action and also shows the growth of their relationship as they learn to trust each other more.
There's 'A Different Path'. This fanfic takes a unique turn where Bella discovers she has some special abilities that Carlisle is intrigued by. It's filled with mystery and some really cool plot twists that keep you hooked from start to finish.
You can start by looking on popular fanfiction websites like FanFiction.net. There are a large number of stories there, and you can use the search function to specifically look for Bella Swan and Carlisle Cullen stories. Just type in their names and browse through the results.