As it is a Victorian novel, the sexual facts are much more implied than stated:
"She had been made to break an accepted social law". An interesting quotation which, to my mind, sums up the relationship between Tess and Alex.
Some clue might be in this significant use of the passive voice. Even considering that Tess might not have undestood, what was going on the first time when Alex actually raped her (for he knew what he was doing) there is an fatal atraction. When he is around she acts as she wouldn┤t in other circunstances. The last of these acts is the murder.