Even though it is all-consuming and can take years to play out, I think infertility (as a condition - not as a mindset) is actually temporary. We will always carry its scars, but the active treatment phase will be over at some point, either as a result of a pregnancy, adoption, or choosing to remain childfree.
But the time that we are in treatment, that transitionary stage during which you endure the rigors of infertility is, as far as I am concerned, purgatory. In Roman Catholicism, purgatory is the third state, between heaven and hell in which souls that are not sufficiently free from sin are unable to enter heaven. They are also not sinful enough (is that like being the Diet Coke of Evil?") to warrant going to hell.
Purgatory is the state of purification for these souls to free them of sin, usually through pain and fire, so that they can ascend to heaven. (Back in the day, you could also buy indulgences to stave off some of the pain of purgatory. I think there is a good argument that infertility clinics are the new indulgences to buy our way out of the purgatory of infertility. They certainly charge enough. But where is our Martin Luther?)
It is always difficult, though, to see those that you came in with leave before you. Even though all of us dealing with infertility have infertility in common, we do not have outcomes in common. I browse through other people's blogrolls and see all of the new positives and discussions of ultrasounds in the first trimester for girls who have struggled for years. It is wonderful to see those who have struggled get to where they want to be, but it also illustrates how transitory this state is. One month could be the difference between being on the infertile side of the coin to being on the pregnant side of the coin. It is also difficult, though, because when you are still on the infertile side, you feel as if you are once again missing the boat. You're not invited to prom. In other words, you're still not pregnant.
I think Tertia put it very succinctly: "those who have succeeded ... know that there is a (happy) ending to their journey. Their journey is finite. Those still trying don't know. They don't know if they will ever succeed." In other words, we don't know when we will get to move on from purgatory to our next destination.
Anyone have some indulgences I can buy to move things along?