The boy's parents are separated. The girl he goes out with is his sister, and the house they go to is their father's. It's the boy's birthday, and the past year his mom had promised him a cake, but due to their situation, she couldn't make it. But this year, she would do everything she could to make that cake for her son.
So, while the boy was playing carelessly with his sister at their father's home, the mom started preparing the cake. It may be a small town, and the small business owners may well know her (as it usually happens in small towns, where everybody knows who is who), and since they trust her, they let her use their instruments for the occasion. Especially knowing her condition. What's wrong with solidarity?
Anyway, the boy is with his father and sister (and step-mother?), and suddenly it's decided that they'll make the boy a birthday party. Because the father's condition allows, he can get him the best cake, and the best party, unlike the mother. So the boy decides to stay and celebrate the birthday with his father that year, possibly forgetting his mother's promise of a cake at home due to the excitement of having a real birthday party.
Meanwhile, after going through all that sacrifice to make the cake for her son, the mother finally finishes, and all that is left now is to wait for the boy to come back home, and celebrate together. But the boy doesn't come. And all that work, all that love, is wasted away.