I think it's great when people are able to move on from a broken relationship shortly after it ends. Sometimes it takes a person a bit longer. And sometimes, a person still grieves for the relationship many years after and wonder why. I don't think there is an appropriate time for grieving a relationship; there are so many factors. You said yourself that you invested a great deal in it. Regardless of what the investment was, I believe you are still allowed to feel the grief. However, if the grief of losing the relationship is taking over your every thought, you may want to consider seeing a therapist if you haven't done so already. Perhaps there are underlying issues that you need to resolve before you will be able to move on effectively.

I've experienced some of what you have said. I've been to therapy for it - it definitely helped, but I think there are some days that are harder even with the therapy.