The answer to this is purely a matter of opinion on your part. It helps to look at the facts surrounding the situation, and your own personal feelings in regards to the moral implications involved as you form that opinion.
August, a lively and dynamic character, in fact, is a violent schizophrenic. His drastic mood shifts come without warning, abruptly, and his wife Marlena is usually the unfortunate victim, along with some helpless animals that end up in his path. When he is in a good mood, he is irrisistably charming, kind, and loving; these traits are what has kept Marlena with him for so long. However, when his mood shifts, it is extreme and frightening. Marlena, unaware of these things when she married him, realized quickly that she had gotten more than she bargained for.
So, does that justify adultery? Were there better courses of action that she could have taken and still achieved the same ends? Could she have gotten a divorce? Would August have granted her one safely, without threatening harm? Did their society condone divorce or separation? And, what role did Jacob play in the situation--should he have stayed away from Marlena? What accountability does he have? Did he tempt her unduly, or disrespect her wishes in any way?
I hope that all of these thoughts help you to start forming an opinion on the matter. It's a tricky situation, filled with gray areas that can be argued either way, so, good luck!
I belive that when August attacked Marlena- she decided to leave him- emotionally, as well as physically. It was at that point that she truly sepearated from the marriage - her heart was no longer in it. Which is what we are saying when we ask for a divorce. To answer this question means to ask ourselves- "When does a divorce truly begin?'
Is it when the paperwork is complete or when one lover has decided to seperate from anothers heart beat? For Marlena no paperwork was needed as her heart was no longer in it. She had decided that with or without Jacob - her marriage was done. The physical act was only an expression of the love she wanted so despearatly to give and have someone know how to recieve in return.