I guess that what is suggested about Lady of Shalott's love towards Sir Lancelot is that her love is impossible. She was cursed not to look at the city below her, yet she did and fell in love with Sir Lancelot, although she knew she could never be with him because of the curse. Her love is thus impossible, and even before she got to meet the love of her life, she died because their romance was doomed to fail even before it began.