Mork & Mindy (1978)

S4E7 Long Before We Met...

Mork joins Mindy at her high school reunion, feeling jealous when he sees her interacting with an ex-boyfriend. In a bid to change the past, Mork decides to travel back to the prom to eliminate the boyfriend from the picture. After successfully altering the timeline, he returns to the present, where Mindy comforts him, reaffirming that he is the only one she truly loves.