Don't Cry Over Spilled Milk- Song

I immediately connected with Christina Rossetti's Song. I took it to mean that there are some things that should never be forgotten, but that shouldn't consume your thoughts. For instance in the first stanza she writes, "And if thou wilt, remember, / And if thou wilt, forget." The person may be dead but their life need not be dwelt upon. There are other things for people to do in their lives besides contemplating a death of a loved one, no matter how sad that death may be, so remember that person and keep them in your heart, but move on. Besides, to sound really pessimistic, they are already dead; no amount of mourning is ever going to bring that person back. That is in fact another reason why the dead person tells her dearest not to mourn; since she is dead, she will never receive that affection.
I believe this can be seen in the later lines as well: "Haply I may remember, / And haply may forget." Since she is dead and mourning is useless, the dearest should forget her and move on. However, they should remember enough to keep the memory of the person alive. In other words, the dearest should remember enough to not forget the dead, but forget enough to not continually mourn over her needlessly. In essence, I took this as a more in depth version of the saying "Don't cry over spilled milk." It's in the past and it can't be changed, so there's no use worrying about it.