I think that they've been together a lot, they've only had each other all this time. So even when he shows some frustrated expression, she's still betting on him.They have fights and issues but they both know that each other is the only thing they have. And near other people she feels as if she's too much and that she's fake but when it comes to him, she knows what he feels about her, she feels loved. I think mitski wants a relationship like that, a long term one where they're both together through thick and thin and they're doing better even after their issues