Isolation is a tricky bird in Brave New World. On the one hand, it's a painful experience for more than one "unique" character who finds himself at odds with the rest of society. On the other hand, it's a means to self-discovery and spirituality. Because of the latter, solitude is essentially outlawed in the novel's futuristic, highly controlled totalitarian setting.
John only "falls in love" with Lenina because she is the first white woman he's seen aside from his mother. He thinks she is the way out of a life of solitude and loneliness.