It was right, or at least alright, to lead the singleton, given that you elected to defend. But you should not have elected to defend.
Partner has at least 12-13 high card points and five hearts for her opening bid. You have 9 high card points and four hearts, giving the two of you slightly more than half the deck (probably), and nine hearts. Given your spade length, the opponents probably have eight, and there would be 17 total tricks under the law of total tricks.
With your preponderance of strength, you are favorites for nine tricks in hearts. The opponents can probably make eight tricks in spades. You should not give them the opportunity, and should shut them out. Even if it cost you down one, it would be worth it to prevent their part score (unless you were both doubled and vulnerable). You should force them up to three spades if they want to declare, because that's where you have a chance of beating them.