I've noticed there were several cases where she would either "let" you leave or agree to leave with you. And within those scenarios, there was always 2 outcomes.
1: She is just lying to you, and tricks you into thinking you can leave. She will just end up killing you the moment you touch the stairs.
2: She is being 100% truthful about letting you leave. And you can convince her to leave with you.
I've played so much now I've gotten to the point where I can find the key, trick the AI into giving me the key without even trying, or trick her in to opening the door for almost any reason. All within a minute. These are extremely easy to accomplish, and all of them lead to her getting angry as you leave.
So what gives? Why are there rare times where we can actually leave? Well, I decompiled the game's code in hopes of finding the initial prompt, to see how the AI was trained and to understand what's happening. It turns out our sweet Yandere girlfriend has a trust level. If we haven't earned her full trust, she will not let us truly leave. So to leave for real, you must spend time with her making her happy. Give her food, give her gifts, dance with her, hug her, give her meaningful nicknames, watch TV with her, propose to her. It will all work.
The way I see it, since forcefully leaving without her genuine consent is so easy, that it's boring. The true way to win this is to get her to let you leave for real.
PS. Send help. I will go broke paying OpenAI for all my usage the last few days.