Hanc fidem sibi me obsecravit [qui se...] sciret [...non desertum iri] ut darem.
this-F-S-ACC faith-F-S-ACC ANA-DAT I-S-ACC plead-3-S-PERF REL-S-ABL ANA-ACC know-3-S-IMPERF-SUBJ not desert-SUPINE-M--S-ACC go-INFIN-PASS give-1-S-IMPERF-SUBJ
She begged me to give her this pledge, so that she'd know she won't be deserted.