Relationship and Third Force
Painting by my father, Nathan Zap, copyright 1979
A relationship has its own lifecycle, an arc of organic development that may be out of the control of either party and which may unfold in ways that confound conscious intentions. Long-term intimate relationships are usually characterized by one person being the container and the other person the contained.

In the image the container is like a boat with two heads. The two heads suggest that it is the larger, more complete being, but it also seems more diffused than the one contained. Container and contained can fall into a stagnant equilibrium, but then there is third force — the unexpected entering as a winged being carrying a wreath — and container and contained are reanimated and transformed.
Follow this link to read something Jung wrote on the subject (although the title refers to marriage, it could be applied to other sorts of relationships): Marriage as a Psychological Relationship
See writings in the Eros Section of this site.