That is why abuse goes on for so long! The partner always believes it won't happen again and they'll "give one more chance". Abusers seldom change without some form of intervention and a lot of support is needed for the person being abused.
I do think the cases are different although I don't condone violence at all. Mary is in extreme physical danger from this guy, he has no control whatsoever over his actions!
The guest girl has been very wary of him all evening, you could tell from the way she looked at him. Obviously his behaviour is well known to their friends.