When it comes to the three cardinal sins, Avodah Zarah (serving foreign gods), Gilui Arayos (acts of sexual immorality) and Shefichas Damim (murdering another human), we are required to choose death [Al Kidush Hashem] rather than transgress.
[allow yourself to]
Being that Gilui Arayos is one of the three and being that improper touching is an extension of Gilui Arayos, Chazal thus teach us that one should rather be killed than allow himself to transgress a sin of sexual immorality, even if only the prohibition of Negiah, touching [a prohibited] female [Derech Chibah, for the purposes of pleasure, love or to get close to her]