Why didn’t Jess want to go to Leslie’s parents’s house?

I believe that this question is asking about events that are narrated to us in chapter seven. The start of chapter 7 has the narrator explaining to readers that Jess finds it odd that Leslie enjoys working with her father so much on weekends. He is especially confused that their "work" often turns into intellectual discussion in which no actual work happens.


Half the time they were supposed to be working they were just yakking away.


Jess finds this relationship so odd and so uncomfortable to be around that he actually avoids being at Leslie's house. Part of Jess is annoyed that Mr. Burke is robbing him of potential time with Leslie.


Jess's feelings about Leslie's father poked up like a canker sore. . . . Lord, that man got in his way. It even poisoned what time he did have with Leslie.


Leslie is quite astute, so she invites Jess to come and work with them one weekend. Leslie hopes that Jess will learn to enjoy the work and the discussions. Jess figures that giving it a try can't hurt, so he agrees to Leslie's suggestion. Jess is somewhat surprised that he actually enjoys the combination of manual labor and intellectual discussions.

There are a number of reasons. For one thing, Jess doesn't really like Leslie's father, Bill; at least, not initially. It's not that Bill's a bad man, it's just that he does seem to take up rather a lot of Leslie's time, time that could be better spent with Jess. At least that's what Jess thinks anyway. We should always remember that Jess is quite a lonely boy, and so without Leslie to keep him occupied, he quickly gets bored. So one could say that perhaps Jess is being a little selfish here; although given the circumstances of his home life it's perfectly understandable.
That leads us on to the other main reason why Jess doesn't want to go to Leslie's house: his non-existent relationship with his father. Leslie and her dad have the kind of close relationship that Jess can only dream about. Being around them together will act as an unwelcome reminder of just how bad things are at home between Jess and his own dad.