

That sounds to me like she doesn’t even know you are infatuated with her, correct? You mention that you never told her you’re in love. What you are doing is unfair both to yourself and to her: If she thinks you are friends, she has no reason to treat you any differently than her other friends. So it’s understandable she might take some time to answer if she’s busy. How would she know you are expecting more of her?
It is unfair to yourself, because you’re keeping yourself in that limbo by obsessing over it. You are expecting her to magically behave in exactly the way you want - without ever having communicated your feelings and expectations. And then you get stressed because another person didn’t behave the way you wanted them to. That’s like getting depressed because the sky is blue and you got it into your head that it ought to be yellow. The only reasonable thing you can do is work on your own expectations and reactions to other people. You have no influence over other people’s feelings, how they behave or whether they like you or not. If you allow things you have no influence over to take control of you so much, you will never be happy in life.
Even if she told you today “I love you” and you get together - how would a relationship work if you can’t even communicate a simple need such as “I noticed you take a long time to answer - is something up? I’d appreciate if you could at least write a short ‘I’m busy, let’s text later’.”
And yes, the people who tell you to work on yourself DO get it. One person not reciprocating your feelings should not throw you into such a deep depression and if it does, you need to work on yourself and not date.
There was a student in my elementary school class in the early 90s, whose single mother worked as a cleaning lady at the school and supported both of them with that money. They had a small apartment, a car and while she was considered poor, she always had enough clothes, school supplies etc.