1. Prince Dies
When Tess accidentally falls asleep, the family horse gets into an accident and dies. The Durbeyfield's now have suffered a tremendous financial loss and Tess, feeling guilt, takes up a job at the D'Urbervilles. This is the start of Tess's troubles. Here she meets Alec, who falls in love with Tess's beauty and begins to pursue her. Alec takes advantage of her and she gives birth to his child, forever making her impure. Her impurity makes her decide to never marry and provide ample resistance to Angel, whom she obviously loves. If it was not for the child, she could have married Angel right away and live a much happier life.
Later on in the novel, she actually blames Alec for all her troubles confirming the importance of the event. "He who had wrought her undoing was now on the side of the spirit, while she remained unregenerate" (p 325).
Tess is angry that Alec could so easily turn from sinner to saint while she will be tainted her whole life with his wrongdoings.
2. Tess Tells Angel the Truth
After Tess marries Angel, she goes through a struggle of whether or not to tell her husband of her child with Alec. Her mother advises her not to, but guilt fills Tess and she cannot help but tell him. She writes a note but he never receives it, giving her a second chance to rethink her decision. She decides her original decision was right and tells him in person. Because of her honesty she loses the only man she ever loved that loved her back. Angel leaves her for Brazil and he becomes among the many men in her life who have wronged her, alongside with her drunken father and Alec. The repercussions...