5/ Different goals and desires
As time goes by, your intimacy develops, and you start having a clearer vision of what both of you want. This vision can be about plans for the future you share, or about different life goals you developed… Which can lead to a seperation! Which is why talking about these question within your couple is paramount, and the sooner the better. Do you want to have kids? Do you prioritize your career? Would you rather move often and travel? Etc…