I understand you want a universal recommendation, but books on relationship psychology work differently depending on what's actually bothering you! Books about relationship games and classic works are definitely the foundation, but I'd first clarify: are you more interested in unhealthy behavioral patterns, or rather self-discovery and building healthy boundaries?
If we're talking about a genuinely useful modern approach, you should look for not one magic book, but a combination: something from cognitive-behavioral psychology (helps you sort out your thinking), something about attachment and emotional regulation, and definitely something about communication. A lot of people nowadays recommend authors who write about how our childhood affects adult relationships - it's genuinely a mind-blowing insight for most people! But besides reading books, what also helps is consciously applying them to your own life, rather than just consuming the information.