Fundamentally, the balance in the relationship is incredibly off and is never addressed properly at all. Wei Xiu may show weakness towards her own feelings and base desires for revenge, but the relationship dynamic is incredibly imbalanced against Puyang.

Puyang is consistently in the dark in the relationship. What prevents this from feeling like a push and pull dynamic is that Puyang very rarely ever suspects Wei Xiu, and the few instances where she does, either Wei Xiu is shown to be completely in control, having contingencies and seeing Puyang do everything exactly as she expects, or Puyang simply brushes any suspicions off near-instantly. The worst part is that many of the times that Puyang brushes off her suspicions, it's a result of Wei Xiu intentionally relying on Puyang's love for her to distract her. This results in the romance taking on uncomfortably manipulative control aspects. This can be solved with a counterbalancing arc or relationship aspect, neither of which end up really happening, or by having a story that's just intended to be uncomfortable, which clearly isn't the direction the author is taking. It also stains the love between the two in a way that desperately wants a counterbalance.

Providing some slight counterbalance is the past-life memories, but this doesn't actually work. The first time Puyang dreams of the past and gains more information, she is already so in love with Wei Xiu and has convinced herself to not doubt her that no lasting doubts result from it, furthering the uncomfortable manipulated feeling. Wei Xiu then gets a past-life dream. This is used in a somewhat reasonable way, introducing further inner conflict for Wei Xiu, but it shifts the focus even further away from any potential suspicions from Puyang and just generally feels rather cheap since there's already a ton of good fodder for inner conflict that could be put to better use. Finally, Puyang gets another past-life dream that fully reveals the secrets that Wei Xiu was keeping from her. This feels like such a cheap way to do the reveal. The especially intelligent Puyang is simply blinded by love and/or outsmarted the whole way through and didn't have hint of suspicion for ages until it's just told to her outright in a dream. Wei Xiu once again avoids a moment of honesty where she fully confronts her inner struggles and brings it out to tackle with her partner.

The final arc (s) take all these problems and escalate them even further. On a fundamental level, using a misunderstanding as the premise to launch the arc is such a cop-out. Technically the much worse option of simply never having a moment of honesty or anything similar exists, but this is probably the weakest reasonable possible way to begin this arc short of that. It feels like this final arc simply completely fails to address any of the actual issues in the relationship. It ends up with the same status quo. Puyang is still the one pouring in all her love. Wei Xiu refuses to be honest just like always, and now she doesn't even have the (in fairness reasonable) excuse of cracks in the relationship opening up outside dangers to her plan or to Puyang. All that's left are the dangers that Puyang can pose to her, and obviously from her actions and thoughts, out of guilt and love she's willing to accept those. The most important thing is that even at this final juncture, it's still entirely Wei Xiu controlling the relationship, Wei Xiu making all the decisions above Puyang's head. It's incredibly depressing to see Puyang effectively still having zero agency when it comes to the important parts of the relationship.

And yet, at the same time, Puyang seems to have to take all the agency and initiative in the less fundamental parts of the relationship. She chases Wei Xiu in the beginning. She coaxes and deals with Wei Xiu as Wei Xiu's inner conflicts cause her to basically lead her on and basically ends up doing the PUA tactic of hot and cold on her. Upon learning all the secrets Wei Xiu was hiding from her and having basically her entire world up-ended, she's the one pushing and wanting to hear the truth from Wei Xiu. When Wei Xiu intentionally hurts her to begin the separation arc, it ends up being Wei Xiu who falls ill and Puyang who trots over and takes care of her. Wei Xiu ends up taking an arrow for her, a frankly already pretty tropey and sudden way to get a partner to show concern, except that Puyang never once hardened her heart against Wei Xiu and has been consistently pouring out her love towards Wei Xiu this entire time no matter what. It's so incredibly offputting, like seeing a wife in an abusive relationship clinging on no matter what (reading comprehension point: no I am not strongly making the point that this is an abusive relationship, I'm describing the feeling it gives off at times).

Finally, an important point to make. The actions, crimes, and/or karma of those people around Puyang make sense to consider for character motivation. However, they do not reasonably contribute to the relationship dynamic being talked about. The issue at hand is not a lack of belief in the actions of the characters in the relationship. It is that a badly balanced relationship dynamic taints the romance and chemistry of the relationship in question from an outside observer's perspective.

Wei Xiu never found out about Puyang's rebirth and Puyang never knew Wei Xiu had visions from their previous lives. I think the revelation would've added more tension/juice to the story and strengthen their relationship. Alas, I'm just a drama chaser.