In Chapter Seven of The Great Gatsby, the narrative reaches its climax. In this chapter Tom comes to hate Gatsby because he realizes that Daisy has been conducting an affair with Gatsby. But what increases his hatred for Gatsby is his belief that Jay Gatsby has killed Myrtle by striking her at a high speed with his car, and he did not even stop.
While Tom is in another room of his house on the phone with Wilson, he is heard saying he will cancel some deal. Daisy suggests cynically that Tom is merely pretending to talk with someone on the phone. Soon, Tom bursts into the room where the others are, sees Gatsby and extends his hand "with well-concealed dislike," saying that he is glad to see Gatsby. When he again leaves the room, Daisy goes over to Gatsby and kisses him, murmuring that she loves him.
After Tom returns to the room, he notices that when Daisy's eyes meet those of Gatsby they seem "alone in space." Then, as Daisy says to Gatsby, "You always look so cool," their eyes meet and Tom discerns the passion between them.
She had told him [Gatsby] that she loved him and Tom Buchanan saw. He was astounded. His mouth opened a little and he looked at Gatsby and then back at Daisy as if he had just recognized her as someone he knew a long time ago.
At the insistence of others, Tom agrees to drive into the city. He rises, "his eyes still flashing between Gatsby and his wife." His hand shakes in his effort at self-control as he finishes his drink. Tom snidely suggests that Gatsby drive his coupé and he will take Daisy in "this circus wagon," as he calls Gatsby's car. Daisy moves away from her husband, declaring that she will go with Gatsby.
As Tom drives with Jordan and Nick in Gatsby's car, he reveals that he has investigated Gatsby and found him to be a fraud. He looks back for his coupé, worried that Daisy and Gatsby may turn down a side street and go "out of his life forever."
Later, at the hotel, Tom confronts Gatsby, "What kind of a row are you trying to cause in my house anyhow?" But Daisy insists that Tom is exaggerating and asks him to have some self-control. This comment angers Tom further. Then, when Gatsby tells Tom that his wife no longer loves him since she now loves him, Tom exclaims, "You must be crazy!" However, as they quarrel Daisy finds her affections returning to Tom because when Gatsby tries to get her to say that she never loved Tom, she hesitates. She cries to Gatsby,"Oh, you want too much!....I love you now--"
Tom promises to take better care of Daisy, and he informs Gatsby that Daisy will not leave him for someone who "hangs around" with Meyer Wolfshiem who is a bootlegger and a criminal in other areas. As Gatsby tries to defend himself, Daisy draws
...further and further into herself, so he gave that up and only the dead dream fought on as the afternoon slipped away.
Tom then tells Daisy to start on home in Gatsby's car because he knows that he has won back his wife, a woman who has retreated into Tom's social position and money.
After Daisy and Gatsby depart, Tom, Jordan, and Nick soon leave the hotel. On the way back, they see that there has been an accident as there are three or four cars at Wilson's garage. Tom stops and learns what has happened; he makes sure that he informs an investigating policeman that the vehicle which struck Myrtle is yellow. Further, he pushes his way out of the crowd and gets back into his blue coupé. Slowly he drives away until he rounds a bend; then, he steps on the accelerator, and Nick hears Tom sob. Enraged, he curses, "The -----coward!....He [Gatsby] didn't even stop his car."
I guess I'm a little confused by the question. Chapter seven is the bulk of Tom's hatred for Gatsby. This is where he learns of Gatsby and Daisy's prior relationship and has to verbally spar with Gatsby to show who loves Daisy more. I'm not sure that any real "hatred" existed for Gatsby until this chapter; he was suspicious of the past, but I'm sure he hated Gatsby yet. Certainly things went downhill for everybody after the hotel fight though.
Maybe you're viewing the ending of chapter seven as a separate incident from the rest. In which case, the belief that Gatsby killed Myrtle would lead to his increased anger..
I think one thing that increased Tom's hatred for Gatsby was the confrontation about Tom's infidelity to Daisy. He doesn't see himself as being wrong for it, whereas he is enraged when he finds out about Gatsby and Daisy.
Gatsby keeps calling Tom old sport which is easily seen as a term of friendship which Tom is not a friend of Gastby