Really you cannot rely on a relationship to cure you. Been there, tried that. Failed miserably and ended trying to kill myself. You can only rely on yourself to maintain your health. You definitely need a support system but no body is going to cure you. You're the one that fights and relying on someone else is a scapegoat way to go about it.
Trust me, I know it gets tiring. I know. It is reallllly ****ing hard. I don't discount that at all because it's simply true. But at the same time, while a relationship cannot cure you you can use it as an excuse.
Not as reason. Don't put that person in charge of your well being because they cannot be responsible for you. That is unfair to them. It is unfair to you.
Use them as an excuse. Meaning if they weren't there you could very well find another excuse but they are there so they can provide a very good excuse for now.
You will always have bad days even if you're stable. There will always be bad moment. That is just life. We may experience them a little more, or a lot more, intense than everyone else but it is just life. Life goes on. You go on. You can go on.
I'm not going to say don't pretend because god knows I do. I save face. None of my friends know my struggle, not even my boyfriend (though it's getting to point where he's noticing things and I will have to tell him).
But understand that there is always tomorrow. Emotions, even though they really honest to god don't feel like it, they WILL end. They WILL subside. It WILL stop. It might start up again. But at some point everything stops. There is always tomorrow. Tomorrow may be better. It might not. But there is HOPE. Tomorrow may better. Hold onto that. Even when you're crying yourself raw or you're laying in bed apathetic or whatever. At some point that exactly feeling will end. Tomorrow it may end.