When things are wretched for you, I am not going to require you to put on a happy face.
I am not even going to require you to think positively.
Right now you are in a state where every demon is running loose. You are grieving a separation, or mourning a failure. All of it is legitimate.
I will demand that you know one thing, no less human than the pain itself — that it is temporary.
Emotions tend to be dictators. They take over your consciousness and sell you the line that it has always been like this and always will be.
And that, my friend, is a lie. You do not build a life on a lie. You do not build a business on false working assumptions. You cannot even cook pasta if you lie to yourself about the cooking time.
So you are grieving at the moment? Fair enough. Pain, like pleasure, does not last for ever.
Put a small note in your right-hand pocket with a small plan on it: what I will do when the pain has passed.
That note is not optimism and it is not a distraction. It is the only piece of work available to you while the feeling is running, and it is genuinely useful, because the version of you that exists after the pain lifts will be depleted, disoriented, and in no condition to plan anything. Somebody has to leave instructions for them, and you are the only candidate.
And at the advanced level: start building bad days into the regularities of your life, and construct a practice for them.
They are not an interruption to your life that you are waiting out. They are a recurring feature of it, they arrive on no schedule, and a person who has a rehearsed response to them suffers a fraction of what a person improvising does.