It is at the end of Chapter Six, at the close of yet another of Gatbsy's riotous parties, that Gatsby speaks to Nick and shares his conviction that Daisy "did not like" his party. We are not told directly why he thinks this, but we are left to infer that his belief that she did not like it is based on the outcome of the party. Note the following paragraph that Nick tells us:
He wanted nothing less of Daisy than that she could go to Tom and say "I never loved you." After she had obliterated four years with that sentence they could decide upon the more practical measures to be taken.
Because the party had not culminated in this statement and happy ending for Gatsby, he therefore believes that Daisy hadn't enjoyed it, which plunges him into the depths of depression as he begins to feel distant from her. The fact that Gatsby says that Daisy did not like the party perhaps says more about him, therefore, than it does about Daisy.