Complex sentence: The preterite (simple past tense) is not etymologically related to "go", but instead "went" descends from a variant form of the preterite of "wend", the descendant of Old English "wendan" and Middle English "wenden".
Split into simpler sentences: The preterite (simple past tense) is not etymologically related to "go". Instead "went" descends from a variant form of the preterite of "wend", the descendant of Old English "wendan" and Middle English "wenden".