Having read the most recent posts here, I'd like to offer "on the beam" as a phrase to describe a healthy relationship. The way this phrase was explained to me was that when a plane takes off and is flying towards its destination, it follows a radio beam. Now, it's not like the plane is "locked on" to the beam and follows one rigid heading; it constantly makes tiny course corrections to keep heading in the right direction, the same way you are constantly moving the steering wheel of your car when you drive. While the plane may never actually BE perfectly "on the beam", as long as it keeps making corrections and stays close, it will get where it's going.
It seems to me that in a healthy relationship (not like I'd know from personal experience, don't think I've ever had one!), you'd be doing that same sort of "on the beam" thing--both parties are headed the same direction but they make continuous little "course corrections" as they may wander to one side or the other. There are deviations, life is certainly not a straight line, but in general, staying on or near the beam allows the partners to grow individually, support each other's individual growth, and share the work of the relationship fairly (maybe not evenly at all times, but fairly based on each person's other work and life demands).
When I put it that way, it makes me wonder why it took me so long to see how "off the beam" XAH and I were, but I did see it eventually, and that is all that counts...