Sforno on Genesis 48:7/ספורנו על בראשית מ״ח:ז׳

1ואני, maybe you think that when G’d said to me: “I will make you into a community of nations,” that He meant that I myself would become the father of more sons but that I was denied those on account of some sin, this cannot be because

2בבואי מפדן, when I came away from Padan Aram, when G’d appeared to me,

3מתה עלי רחל, as the sages say (Sanhedrin 22) a woman’s death is felt first and foremost by her husband; [hence the justification for Yaakov saying עלי, “for me,” i.e. the loss was mine. Ed.]

4בדרך בעוד כברת ארץ לבא אפרתה, immediately after G’d finished speaking to me before I had even arrived at Beyt Lechem, ואקברה שם בדרך אפרת, and I had to bury her there on the route to Efrat; I was so overcome by grief at the time that I did not even have the strength to transport her remains to the burial grounds in Beyt Lechem. There is no doubt that ever since her death my heart was so full of grief that my libido had completely ceased to be active and I would not have been able to sire more children and to thereby become dirtied by sin, even if I had felt the desire to do so. [The author describes the act of procreation as “sinful,” meaning that even among the most pious, the act of ejaculating is itself accompanied by some impure thought, a degree of physical gratification. Ed.].