Ignorance is Bliss
So it goes: knowing brings unhappiness, while ignorance brings happiness. Even an ostrich's happiness is still happiness.
I accidentally saw my partner's chat history on their phone and discovered they were flirting with someone else behind my back.
The OP spent nearly 200k RMB on his girlfriend. Her best friend urged them to break up. Meanwhile, the girlfriend was chatting with a male coworker without revealing that she has a live-in partner. In her conversations, she subtly hinted that the OP was unemployed and had no future. The coworker said something like, "I wish I had met you sooner," and she didn't reject it—keeping the ambiguous vibe going.
This is similar to the plot of the Korean drama "Spring Night." Whether it's developing feelings for someone else or turning the relationship into a transactional博弈, the relationship has already soured. (People with strong moral compasses might want to skip this.)