The tall man/engineer starts frequenting the bar and tries to get Tereza to come back to his place. At first she resists, but then she realizes that she is being sent to this man by Tomas. So by going, all she is doing is following Tomas's command.
Tereza wants to go to his apartment and get to the border of infidelity without actually having sex with him. She will wait until he makes his move, and then she will say, "It was not my choice" (4.15.6).