Do you have book recommendations for healthy relationships?

I’ll preface this by saying I’m currently in a loving, trusting relationship and we’ve recently made the step into ethical non-monogamy. Over the years I’ve read a few titles like happy (derren brown) and self deception (the arbinger institute) which have all been fascinating and certainly helped in my development. They’re not relationship books per se but definitely helped me reframe my interactions with others.

I’m curious to know if any titles out there have resonated with you in your own journeys (regardless of relationship dynamics) and why.

Thanks in advance.