You have a toxic coworker and incompetent boss. Get out.

There are some very good answers here; however, I feel that the odds are stacked against you, and your best bet is to look for a new job.

Take this for example:

Just an hour before the official meeting, Stacy goes in the office of my boss and talks for half an hour with him. At the meeting with my Boss he suddenly told me that my raise won't be possible and that he changed his mind.

Since Stacy had no way of knowing that you were asking about the raise, it looks like you boss wanted to run this by Stacy, which is complete incompetence on their part, and Stacy is running the whole show.

I have been in a situation, where weak/incompetent manager relied on their favorite dev for everything, and I only regret not getting out earlier.

You have a toxic coworker and incompetent boss. Get out.

There are some very good answers here; however, I feel that the odds are stacked against you, and your best bet is to look for a new job.

Take this for example:

Just an hour before the official meeting, Stacy goes in the office of my boss and talks for half an hour with him. At the meeting with my Boss he suddenly told me that my raise won't be possible and that he changed his mind.

Since Stacy had no way of knowing that you were asking about the raise, it looks like your boss wanted to run this by Stacy, which is complete incompetence on their part, and Stacy is running the whole show.

I have been in a situation, where weak/incompetent manager relied on their favorite dev for everything, and I only regret not getting out earlier.