Consolation denied

This short write up attempts to explicate a seemingly enigmatic midrashic assertion

Reuven returned to the pit, and, behold, Yosef was not in the pit; and he rent his garments. He returned to his brothers and said, "The boy is gone! And I, where will I go?" (Bereishis 37:29-30)

Rashi quotes a midrash as saying that he had gone to repent for messing with Yaakovs bed, begging the question as to why now of all times was he involved with penitence for that action?

I would like to proffer that Yaakov—having recently suffered the tragic passing of his beloved Rachel at a young age—had moved his bed into Bilhahs room in a quest for consolation. Bilhah, as Rachels personal attendant, kept Rachels memory alive, allowing Yaakov a modicum of solace and succor. Rachels presence lingered on in and infused Bilhahs space. Consolation by association, if you will.

Reuvens brash and rash action—albeit in defense of his mother Leahs feelings—deprived his father of that small measure of comfort.

Yaakov, denied Bilhah, still hurting and pining for Rachel, proceeded to preoccupy himself with Rachels child Joseph in a secondary attempt to console himself over Rachel through her child. 

(See Rashi's comment to Bereishis 44:29 regarding Yaakov potentially losing Binyamin: והורדתם את שיבתי וגומ' – עכשיו כשהוא אצלי, אני מתנחם בו על אמו ועל אחיו. ואם ימות זה, דומה עלי ששלשתם מתים ביום אחד)

That favoritism, in turn, led to the brothers hatred of Yosef, and, ultimately, to their selling him down to Egypt.

Thats when it all hit Reuven and he realized the terrible unintended collateral damage he had caused and he proceeded to repent for it in earnest.