Maybe it is only an unfounded believe.
The emotion behind close friendship has a own psychology. Companionate love, does not literally contradict the theory of reciprocal altruism, but it does embody an elastic version in which the emotional guarantors - liking, sympathy, gratitude, and trust -are strechted to the limit.The facts of companionate love are clear enough, but why did it evolve?
Anyone can suffer a reversal of fortune, especially in a harsh life of a forager. Once abandoned, a stricken forager is not lon for that world.
One strategy is to make yourself irreplaceable. Another is the association with people who benefit from the things that benefit you. Merely by going about your life and pursuing your own interest, you can advance someone else's interests as a side effect...
that's just theory. :D