Rashi on Genesis 38:11/רש"י על בראשית ל״ח:י״א

1‘כי אמר וגו FOR HE SAID etc. — that is to say, he pushed her off with a straw (i.e., he put her off with a lame excuse) because he never intended to give her to him in marriage

2כי אמר פן ימות FOR HE SAID LEST PERADVENTURE HE DIE — She is a woman of whom it may be presumed that the men she marries will always die young (Genesis Rabbah 85:5).