I recall reading a piece that suggested that in life, we all have about 3 "great" partners - three relationships that are long-ish term and work out in some sense - sure, there are lots of other potential partners, some short-term arrangements that work out well, but I think three, maybe four partners in our lives truly "work out" in any long-term sense. Which is not to say all other relationships are of no value - we can always learn, always grow, always benefit someone else and be of benefit to them - and, well, all relationships end in some way - even in a long-term partnership that lasts many years, one partner will inevitably die before the other.