The singer is overwhelmed after losing someone he sees as his best friend. He cannot make sense of what has happened and repeats that he does not know what to do. Crying seems to offer some relief, but his grief and confusion keep returning.
โMy cup is running overโ suggests that his feelings have filled him beyond what he can contain. The image is usually associated with having plenty, but here the overflowing cup feels like too much emotion rather than happiness. Repeating โcry, cry, cryโ gives the song the sound of someone trying to release that pressure. Calling the lost person โthe best friend that I ever knewโ makes clear how important the relationship was.
The lyrics leave some details open: they do not explain how or why the person is gone, or whether the loss is a separation or something more final. The singer also says he is mad, which may mean anger mixed with sadness, though the exact reason is unclear. Overall, the song presents grief as messy and repetitive: crying may help briefly, but it does not immediately resolve the loss.