Seconding what decan says about Lenormands being read in association with one another. I wouldn't do a single card draw, myself, and frankly I don't find two-card draws to be satisfying, either. An odd number of cards is best for a yes/no. (I realize we don't have your actual question, but read on.)
That said....
The Letter is a neutral card. So if it is your one card in answer to a question about a romantic interest, you aren't getting a strong positive or negative; I'd say lukewarm at best.
The Letter can lighten cards up, suggesting a more superficial level of the card meaning it modifies. As a singleton, I would say it's not very encouraging of the romance, but I would not want to read into it or say more without a fuller spread.
As a further thought exercise, Querent asks "is X interested in me?" The draw: Letter-Fish. Answer: X is interested (qualified "yes" - 1 neutral card plus 1 positive) superficially (Letter), but has many of these superficial interests (Letter-Fish).