I think you are referring to the following "..fact, a man's [i.e., a person's] sexual choice is the result and sum of his fundamental convictions.Tell me what a man finds sexually attractive and I will tell you his entire philosophy of life" (p. In the early Objectivist movement, many people understood this principle to mean that one should only be attracted to people who were Objectivists in their explicit philosophical convictions.
Most people do not act consistently on their conscious religion or philosophy, and indeed most do not really take abstract ideas very seriously.
What we respond to in others in friendship and romance is founded on sense of life.
We don't love someone because they say they are productive, we love them because we see their wonderful engagement with the world and their proactive attitude toward their values.
We don't love somebody because they say they are an atheist, we love them for their down-to-earth attitude to life.
We don't love them because they say happiness is the ultimate value, we love them because they are joyful and give us joy.
However, there is an attitude among secular Americans that one can be indifferent to one's lover's religion or philosophy, or that abstract ideas don't really matter.
Well, they do matter, because they are what we use to consciously guide our actions.
If we take our ideas at all seriously (and total indifference to ideas is not healthy or attractive), we will tend to try to live up to them.
Our sense of life will gravitate toward the ideals we prize consciously.
So any serious relationship with someone who embraces ideas at significant variance with Objectivism would probably be at best uncomfortable for an Objectivist.
In my personal experience, I find most Objectivists are happiest in relationships with someone who is in tune with their values.