In my opinion, it is the individual who is ultimately responsible for their own actions - regardless of who or what provokes them to a state to be capable of such crimes/actions. Having not seen the movie, I do not know what provoked the woman to have the affair to begin with, but the husband had several choices in how he could deal with his feelings of anger and betrayal of the act of infidelity.
When it comes to infidelity, if the marriage was a good marriage, the reason for infidelity begins with the needs of the one being unfaithful are not being sufficiently met to the point they make the choice to be unfaithful when meeting someone who fulfills those needs. If this was the case in the movie - the wife's needs were not being fulfilled by her husband which created the scenario where she would consider having an affair - then one could argue that the husband was the one who "drove" his wife to have an affair which in turn "drove" him to commit murder - where by that "logic", the husband drove himself to commit murder by being the one who initiated the sequence of events which let to the murder.
Assuming we don't know the reasons why the wife had the affair in the first place, let's focus on the choices the husband could have taken. He could have chosen to forgiver her and let his anger go, he could have cheated himself to "get even", he could have chosen to go into counseling to see if they could resolve whatever marital issues existed that may have driven the wife to cheat in the first place, he could have hired a lawyer to divorce her, etc. Instead, the man chose to deal with his anger/betrayal by committing a violent act which resulted in the death of another human being.
Unless the man had some chemical imbalance in which he was not responsible for his actions (like he was an undiagnosed schizophrenic, etc), then he made the choices that resulted in getting to a mental where he was capable of murder. You could rationalize the murder by saying it was the wife's fault for provoking him (which is what lawyers do during trials), but ultimately it was his choice to allow himself to reach that state of mind to commit the act.