Another interpretation: Why did he weep? Because he foresaw that she would not enter with him into burial. For she said to him (Genesis 30:15), "Therefore he shall lie [with you tonight]" — "with you he shall lie [in death], but with me he shall not lie."
Jacob Wept Because Rachel Would Not Lie Beside Him in the Grave
Yalkut Shimoni on Torah 124:5
דָּבָר אַחֵר, לָמָּה בָּכָה, שֶׁרָאָה שֶׁאֵינָהּ נִכְנֶסֶת עִמּוֹ לִקְבוּרָה. דְּהִיא אָמְרָה לֵיהּ "לָכֵן יִשְׁכַּב" וְגוֹ' עִמָּךְ הוּא דָּמִיךָ, עִמִּי לֵית הוּא דָּמִיךָ.