Don't write a novel. Or rather, don't aim for a novel. Write a story. Or two. Or a hundred. Your stories don't have to be complete, they don't always need a final solution to the problems, and they don't need to be long. You can leave them open ended.
Once you find a story that you like and has developmental potential, then look forward to expanding that story into a novel. Introduce new subplots (i.e. the focus of the story is about a hard working mother with a daughter. It focuses on the everyday routine that the mother makes every day. However, the mother thinks that someone else is replacing her daughter, more and more each day. Why is this happening? Who is this new person? She no longer looks like the daughter the mother once knew, but still carries the same mannerism.) Story ends. The story is focused in that strange sensation. That feeling of someone close being replaced by some stranger, but who still feels the same.
Well, let's introduce a new story line, with this as the conclusion: she finds out that she actually has Alzheimer's, repeating each day while forgetting about the others. As her daughter age, she no longer recognizes her daughter without her daughter acting like how she was as a child. The focus here would be the build up on finding out the reason of the strange change. Build up to find out about Alzheimer's.
Want to continue? Well, introduce a small fact about the father. You may need to revise your first story to introduce a small detail about the father. Maybe a pearl necklace the mom always wears. Or a worn-down bracelet, spiralled with black and yellow threads.
Before you know it, you have a novel, started from the story.
Additionally, you can throw in the details to expand a story. A scene about a ball room dance, two paragraphs long, suddenly becomes 2 pages describing the magnificent dresses, party gossips, arrival of x and y princess from z kindgoms.
Cast out your seeds as one-shot stories. Let the ones that grow into saplings become short story. Let the ones that grows into full trees become novels.
One step at a time. Any genre. Any style. Experiment. Find yourself. Find your way. You may also come to find that tending this garden of stories isn't for you. That's okay too. You've learned how to grow a garden. That takes work. Be proud and move on. But don't let your reason to write be because of "he wanted me to write." You're not in love with that person. You're not interested in that person. It now becomes a chore, a work. Work becomes tiring. Things will seem unfair--little things, to be exact. You'll lose that drive, that motivation; and with that motivation, that imagination.
Write to show us the worlds that are in your head, the messages you want us to hear. If it resonates with us, we'll come. And when we do, we'll read. So until then, write. Write away. Not because someone wanted to collaborate with you; nor because someone is telling you they want you to write. Write because you want to. You may find that there are stories you don't want to share. That's okay too. You're finding you. Write away.