In Hamlet, whom are the gravediggers digging a grave for? Why might Hamlet have decided to throw off his disguise at the gravesite?

The Gravediggers are digging a grave for Ophelia. They argue whether Ophelia killed herself or not and if she deserves a sanctified burial. Hamlet is a passionate guy. He frequently throws caution to the wind when he can make an emotional speech about his feelings. Hamlet also carries guilt about the way he has used Ophelia to his own ends.