Honestly yeah, I do think people throw that saying around to avoid dealing with other people's problems and feel like they did something. Not everyone, but people will definitely spit out platitudes to make themselves feel better and claim it's for you, without offering any real form of help or support.
Mental health doesn't get better on its own, nor do illnesses simply go away. They require treatment and lifelong management. If it's not an illness but your life situation that is the problem, then that's what needs to change. And if it's a bit of both, as is often the case, you need real support and motivation to find out what kind of changes need to be made and to keep you on the right track. You need a network of people who will be willing to give you more than a passing "It gets better" as they go on their merry way. Telling people it gets better doesn't make it better. Hoping it will get better won't make it better, either.
And yeah, good times and bad times come and go; things might seem like they're getting better, then suddenly come crashing down all over again, only to repeat the cycle. Some of that crashing is avoidable through change. Some of it is just life, and getting through those parts is about managing your actions and reactions, and how you view your situation. Same for mental illness of any kind. Even with treatment and upkeep, there will probably be symptoms. It never just all goes away forever. This is why genuine support from people you trust is essential, and why you should always communicate what you're going through. If you feel like they're not listening and just jerking you around or trying to get you to shut up, call them out on it. Maybe it's true, or maybe they think they're helping and they just need to change their approach. If you reach out to someone and they don't seem like they can or will help, find someone else. Talk to a professional; it may just be them doing their job, but they will have insights and access to resources that friends and family usually don't. They also aren't going to get worn out from hearing your story. A professional who knows what they're doing isn't gonna just tell you what they think you wanna hear. They'll help point you to what you need.
Also, sometimes it's good to just take a break. You sound like you're really burnt out and it's contributing to the problem. If you can make the time to just fuck off from everyone for a little while, rest, and make some sort of action plan (whatever you think would be best for you at the moment), that might help. Then you can go from there.