Gaslighting, throwing under the bus, passive aggressiveness, flat out ignoring, petty..... how do I get out

Context: first job out of college and interned with the group, my associate is extremely good at their job, which is why I decided to return. Figured if anything I would learn a ton from them.

Well I'm about 10 months in now... and turns out that the OPPOSITE is true ... associate is too much of a control freak to actually let go of any responsibility. On top of that, my actual boss travels so much that my associate is essentially the acting boss.

If i ask a question... GUARANTEED i'll get a passive aggressive answer somehow implying, how are you so dumb that you don't know this. Somehow feel worse after asking a question than before. SO basically have stopped asking my associate directly, and literally asking anyone else for help.

Also constantly blamed for random things I wasn't even around for... like some files that have been off since 2012 that have been exactly the same way since (???). If i try to push back, the response is always, "I don't know what you did to the file, but its wrong and you need to fix it." Nice. Also, every now and then will roast me in front of my boss, really strange dynamic.

A couple other pretty messed up things... maybe i'll go into details one day after I leave. But basically just an extremely toxic environment that has me literally thinking about quitting at least 5-6 times every single day.

When i talked to friends in banking, the consensus I get is that there are shitty people like that everywhere, but in banking (once you've proven yourself), you might get more of a say/get to choose who you work with. And everyone avoids the assholes. With my team, i have no choice but to take their shit day in and day out.

QUESTIONS for y'all.
1. After talking to everyone under the sun about this dynamic, I know its not normal. How do i start interviewing without them noticing (and escalating to my boss)? We all sit on an open floor plan, and basically everyone shares about their person life. Any good reasons why I need to leave for 3-4 hours at a time??

2. What do I say to my boss? She's actually really great, but I never get to interact with her. Part of me wants to do a complete dish out of everything that's happened during my exit interview, but that's probably not good. At the same time, i think she needs to know how shitty of a manager the associate is. How do I convey this without burning bridges?

3. Associate is going to hate me the moment they know I'm leaving. How long of lead time do I give them about leaving? A week? That one week might be the most miserable week of my life (knowing what my associate is capable of). At the same time, I don't want to do my boss dirty with just one day. Any suggestions?