Some take work and. Some don't, largely based on the degree of positive emotional chemistry present or absent. Relationships become work as the degree of positve chemistry decreases. However, even a strong relationship with lots of good chemistry should never be taken for granted but regularly nurtured. Trying to force a relationship into a desired structure is even harder work. Relationships can't be structured.
Possibly. Relationships between two people with different personalities are complex. I think the best answer is that it is a combination of structure and spontaneity that eventually dictates the term of one's relationship. Its important to be yourself and be flexible and understanding towards your partner. Excessive structure can lead to rigid behaviors that can be poisonous for the relationship.