Why does john proctor do when abigail accuses mary of witchcraft in act 3

The Crucible is a 1953 play by American playwright Arthur Miller. It is a fictionalized story about the Salem witch trials of 1692-1693.

In Act III, we see the trial of Martha Corey. John Proctor arrives with Mary Warren and is informed that Elizabeth is pregnant, so she will not be executed until the child is born. John submits Mary's deposition, declaring she was forced to accuse people by Abigail. Abigail, however, denies Mary's assertions, maintaining her story. She then accuses Mary of bewitching her with a cold wind.

John ends up losing control. He verbally attacks Abigail, and then confesses their affair. He claims that Abigail wanted to take Elizabeth's place in the household, and so, wanted her to hang for witchcraft.

may i ask what topic?