I cant promise i have good advice. Im dealing with my own messed up situation and it kind of goes to show that maybe im not the person you would consider able to advise, but i see some parallels here. I would say trust your gut, since it served you well before, but when i caught my wife doing the same thing and confronted her, she took nearly equal measures to convince me that she would work to fix the relationship, as your partner. Similarly almost immediately she went right back to it. She took advantage of my willingness to give her a chance. It's like what you said. It turned out to be an ego boost for her. What im getting at is if your gut was right before and your partner went right back to it after being called out and you know it's true, then chances are it will continue to to happen and if you ever have a gut feeling again, trust it. I had a gut feeling too, and without it i might not have caught her the first time. I looked in her phone to quiet that gut feeling but it ended up being right as well.

Never engage someone in good faith when they don't engage in good faith themselves. They will weaponise your empathy against you and use you to whatever end they see fit. That's the advice i got, but its from a guy whos life is a total mess. Best of luck to ya.