Might be unconventional here, but I’m currently reading More Than Two by Franklin Veaux and Eve Rickert.
While the book has a focus on making polyamory work, it’s also written in a way that anyone could profit from it, really. Even monogamous relationships. It places a lot of value on self-growth, self-awareness, skills that are important in relationships no matter if platonic, romantic, monogamous, polyamorous… even skills that are valuable in standing up for yourself in the rest of your life outside of relationships. It adresses how to counteract and work on your fear of abandonment/being replaced/of loss, and talks about how jealousy comes to life and what to do to work through it. It underlines how to not treat people like your need-fulfillment machines and how to consider their emotions and stop controlling them, while starting to learn how to feel fine being alone or without them as well - to learn that you can be happy without them, to not be too needy or clingy. There’s also a part about worthiness and how to learn to feel worthy, and how to be vulnerable and feel worthy enough to let connections happen. It places a lot of emphasis on the fact that the qualities you want to have (like compassion, for example) are things you work on and are visible in your acts, it’s not inherent to you and it needs practice.
This is just a small part of what this book is about (I’m only at page 100 from ~450), but maybe this is intriguing to some of you already. I feel like a lot of what’s written in this book, at least in the first 100 pages, also sounds kind of stoic in its approaches on how to handle feelings and take responsibility for them, as well as striving to act in a virtuous, ethical manner always. And I read The Daily Stoic by Ryan Holiday every day, which offers a quote from a historic Stoicism personality daily and a few lines of thought to go with it, so it fits in well.