Good evening lads

Could somebody explain the difference please:

—My old good friend, how could I have forgotten you?
—My old good friend, how could I forget you?

Because I see them as being ambiguous:

—My old good friend, how could I have forgotten you?
1)How is it possible that I was actually able to forget you
2)I am not able to forget you because I see you every day

—My old good friend, how could I forget you?
1)It is impossible for me to forget you because I see you every day
2)How did I manage to forget you