There are several negative relationships that appear throughout Fahrenhet 451. One example, as you stated, is Mildred and Montag. However, Montag and Beatty's relationship is also negative because it is based on fear and lies. Another negative relationship would be between Mildred and her friends (Mrs. Phelps and Mrs. Bowles). The relationship between Mildred and her friends is detrimental and negative because they are not emotional attached to one another and, thus, do not care about one another. They are considered "friends" because they enjoy the same programs and have the same views on society. However, their relationship is superficial.
There are only a few positive relationship throughout the novel. A couple of examples would be Montag's relationships with Clarisse and then later on Faber.