Rabbinic Kabbalistic sources provide a different explanation.
First, the primordial sin was about the forbidden relations between Adam and Eve, hence its association with sex. In (rabbinic interpretation of) Biblical Hebrew, eating (אכילה) is associated with sex, and eating the forbidden fruit transformed into having forbidden relations with Eve.
The action took place on Friday afternoon, right before Sabbath. The divine plan envisioned the holy day of Sabbath as the perfect time for the first night when it could be done in holiness (without submitting to one's urges and without the involvement of evil forces, that control the weekdays), hence the rabbinic tradition of having relations (exclusively) on Sabbath eve.
So Adam failed to wait and the sex was somehow "contaminated" with evil forces, and that's how the boys Abel and Cain came out somewhat defective.
Second, in order to atone (after experiencing God's wrath), Adam left Eve and went to... dip himself in the Gihon river. As you remember, semen is a source of ritual impurity and one is commanded to immerse in a natural water source to cleanse himself.
Technically, Adam did not worry about the commandment, because by having two boys (and commentaries add twin sisters) he technically fulfilled the commandment of being fruitful (acc. to Jewish Halachic standards).
Third, Adam liked the waters so much, he spent 130 years pleasuring himself in the Gihon River, remembering how beautiful Eve was, wasting seed, and creating all kinds of evil forces, demons, angels, and whatnot. This narrative is frequently used to explain where did all the evil come from, but it misses the point of #1.
When he finished (I mean ended) those 130 years, he made full repentance, returned to Eve, and begot Seth that was a Tzaddik.
I only forgot the interpretation of the number 130.