Why do I feel worse weeks after the breakup than on the day?

In the first days, shock and adrenaline carry you. Friends rally round, you're busy telling people, and the reality hasn't fully landed. A few weeks later, the support thins out, everyone assumes you're getting better, and the loss finally reaches the parts of you that were numb. That's why so many people feel worst a few weeks in. The dip is the grief arriving properly, and it means you're working through it rather than avoiding it.