Hmmm... it still seems pretty vague to me. It's a little confusing as well as the riddle clearly relates to both the answer and Tifa. There isn't a clear distinction between either.

Oh, My Dearest Love
As previously stated, this refers to Tifa.
The Secret Thing You've Been Hiding
Which "you" is this one? Tifa or the answer?. If we assume that it's Tifa then I suppose the main thing she was hiding was the truth about Cloud's past.
Lost in memories, but still so close
Cloud has a lot of memories, some true and some false, but he is close to finding the truth.
If I Look, Will I Find You
This relates to the answer so maybe it is the truth about Cloud's past?
If I Find You, Will I Lose You
If Cloud discovers the truth he may have lost Tifa.

I'm sure this has already been guessed but I'm going to go with simply... the truth about Cloud.