Too many flaws... (contains spoilers)

Very interesting film, but too many flaws in the plot, or rather situations which are not explained or insinuated convincingly:

if Jacob had really seen his wife and her lover together, why didn't he confront them, beat up the other guy and kick him out of the house, or at least talk to his wife about the affair shortly afterwards? How could he not have known the identity of the other man?

Okay, I can understand that Jacob was seeing a therapist on account of his sense of guilt, but why did he have to choose his lover (or was he just imagining that?)? Was she actually a therapist, or was she pretending to be one, or were the therapy sessions all in Jacob's mind?

What was the secret that Jacob's father in law was on the point of telling his wife? Did he also know about Jacob's affair? Not really clear.

I had the impression that Vincent Gregory was practically stabbed to death, yet we later seeing him getting out of Jacob's car, not particularly distressed and certainly not covered in blood as he was before. Is this once again Jacob's imagination?

I think that if these details had been clarified a little more, the film could have been much more convincing.