Willy and Biff have a troubled relationship. Willy's grandiosity and refusal to live in reality have almost ruined Biff's life. During the course of the play, Biff comes to terms with this reality as he tries to change his life and steer a psychologically more healthy course than his father's.

By the time Biff is a teenager, it must have been apparent to Willy, whether he wanted to admit it or not, that his dreams of being a wealthy salesman sitting in a hotel room in his velvet slippers as the telephone orders came flooding in is not going to be his reality. In truth, Willy is a mediocre salesman struggling to survive economically. Therefore, he pins his hopes and dreams on Biff.

He decides that Biff is better than other teens and will have the success he never had. Because Willy defines success as using your personality to dominate others and fast talk your way to wealth without having to do the hard work of gaining expertise, Willy pushes this way of living on his son. He doesn't encourage him to work hard in school and instead praises shallow "values," like popularity and putting things over on people, such as through petty theft. He never encourages his son to go to college. He also badly disillusions Biff by having an affair that Biff becomes aware of in high school. Biff is not impressed by, but instead is angered and shattered at his father's deceptions and betrayals.

Biff tries to get across to his father during the play that he has himself wasted many years being misled by his father's delusions but now has every intention of accepting being an ordinary person and living in reality. He has seen the destructive quality of his father's desire to be bigger and better than everyone else, turning life into an endless, pointless competition.

Willy, on some level realizing he has been a miserable failure, tries to make things right with Biff the only way he knows how, which is to commit suicide so that Biff can inherit his insurance money and have a fresh start.

The relationship between Willy Loman and his son Biff isn't a good one, and that's mainly because each one has, to some extent, disappointed the other's expectations. Willy had always wanted Biff to be a high-achiever, to become “a well-liked man,” which for him is just about the most important thing in life.

Initially, it seemed that Biff was going to do his old man proud and become a star football player. But after he flunked his math test and missed out on a football scholarship, his dream lay in ruins.

But it takes two to tango, as they say, and Willy disappointed Biff. When Biff found out that Willy was having an affair with a secretary, such was his trauma that he went completely off the rails. In fact, he was so hard-hit by his father's infidelity that it affected his school work. It's no exaggeration to say that Biff's flunking of his math test and missing out on a football scholarship was the direct result of his father's transgressions.

As a result, father and son have a very bad relationship. Willy can't help but remain disappointed in Biff, and Biff can't respect Willy, not just because of his philandering, but also because he's become something of a dinosaur in the world of sales even though he still acts like he's a hot-shot.

The relationship between Biff and Willy can be described as turbulent, dysfunctional and, actually, dissociative.

It is turbulent because the history of angst, secrecy, and disappointments between Willy and Biff prompts instant arguing and fighting between the two men, at any given time.

The angst on Biff's part comes from the disappointing discovery of his father's affair with "The Woman." This discovery occurs during a time in Biff's life when his high school successes have just come crashing down, and he needs the support of the very man who builds him up and puts him on a pedestal.

Knowing that this very man, his father, is capable of lying and deceiving puts Biff in a diatribe: IS he the "wonder child" that his father, the liar, has made him out to believe he is, or is Biff Loman yet another one of Willy's "lies"?

On the other hand, the fact that Willy knows how Biff feels about him after the discovery is a huge bad blow to his ego: he no longer has his "wonder child" to boast about, and he can no longer continue his project of making Biff everything that Willy wished he could have been. Hence, the men's communication falls apart and seems to only lend itself for conflict. 

The relationship between Biff and Willy is dysfunctional because it lacks the defined boundaries and limitations of affection and mutual respect that should exist between a parent and a child. In a healthy parent/son relationship the father nurtures the son and lets him develop according to the child's own possibilities. Willy does this, but not altruistically: he builds Biff as a more handsome, more talented, and more successful version of Willy in order to vicariously re-live his lost years.

As a result of the lack of proper boundaries between father and son, Biff sees his father as his rival and enemy during trying times. Rather than trying to seek a reconciliation that would enable them to move forward, they basically go head-on against each other like if they were not even related. This is the epitome of a dysfunctional parent/child dynamic. 

Finally, the relationship is dissociative because both men have lived, either in denial or in complete dissociation, of the reality of their lives. Their lack of focus on themselves as individuals, makes it impossible for them to view themselves as part of a healthy relationship. Willy sees himself as a hot shot salesman, sees Biff as a hot shot football player, and sees his American Dream fulfilled. As a result, Biff starts to be sucked into Willy's dream and ends up believing the same things...until reality hits Biff and he realizes that his life had been a lie, all along. Hence, Biff moves out West trying to find himself. However, as he himself says, "something" always brings him back. 

Therefore, dissociation, turbulence and dysfunctional roles constitute the backbone of the Loman's relationship. It is a relationship that can only be healed by the a reality check, and by the mutual choice of accepting it the way that it is.