@Felthry @artemis the "were" in "he were (subj)" and "they were" used to be different! in this case, you have to go back to proto-germanic (btw an old language is "proto" if it wasn't written, but its forms are deduced from its descendants)
anyway in this case, the forms in question were "wēzī" and "wēzun" respectively. over time the suffixes got worn down until the words ended up identical (the z→r change is kinda common too. it also happened in latin)
look at all these forms that got worn down to, what, five? https://en.wiktionary.org/wiki/Reconstruction:Proto-Germanic/wesan%C4%85#Inflection maybe you notice there is nothing that looks like "be" there. because haha just kidding "to be" is actually the result of two older words merging and there's even more https://en.wiktionary.org/wiki/Reconstruction:Proto-Germanic/beun%C4%85#Inflection (edit: i should mention if you go even FURTHER it's actually three words which is why "is" and "was" look so different too)
@niss @artemis it also happened with the copula in Latin too, with at least three words i think?, which is why you have such disparate forms as "sum", "est", "eram", and "fuī"
-F