https://www.etymonline.com/word/be
PIE *bheue- "to be, exist, grow"
https://www.etymonline.com/word/am
PIE *esmi-, first person singular form of root *es- "to be"
https://www.etymonline.com/word/was
PIE *wes- (3) "remain, abide, live, dwell"
And the merger of all these forms in English from different verbs happened around the 13th century, not because of some pre-linguistic history.