Continuing on with the topic of baby and toddler sleep, I thought I would recommend a book.
If you haven't noticed already, I am a fan of John and Julie Gottman's work. The theory they use is based on his decades of research about couples and what makes them happy coupled with (sorry about the pun) her years as a couples therapist. But, more importantly, the ideas are easy and straightforward. Like, the idea of "love maps" which is basically the idea of making sure you continually work to know each other. They even make love map cards to make it into a game. Also, "rituals of connection" which emphasizes the little and big rituals of relationships like going on vacations together, going on regular dates, and kissing each other goodnight.
The authors use the Sound Relationship House theory which is what is taught to us therapists for improving a relationship but is written in an accessible way for the reader. (We all know that accessibility is important especially if you are a new parent with very few hours to spare). There are lots of stories about couples and examples of how to strengthen relationships.
I wouldn't recommend using this book in place of therapy but it would be helpful if you are a soon-to-be or new parent.