Most couples make the mistake of thinking they know their partner and then stopping asking questions. Your partner is growing and changing, as are you. Sometimes it is subtle and incremental, what James Clear calls "atomic changes" which add up over time.
Talk about the basics and build the habit of daily check ins to keep you connected. Gottman has a whole video on the Magic 6 Hours a Week - how to stay connected and build your relationship.
Does one person tend to call on the phone more?
How does the partner interpret that?
Is one person more cluttered and disorganized or messy than the other person?
How does that impact you?
As with each of the preceding questions, tell your partner what you need from them, rather than complaining. Little by little, improve your connection and move towards a union.