Isn't the whole point that fated mates are so rare that majority of people will never meet theirs though? So most people end up with someone else anyways, because fated mates technically aren't actual mates until they bite each other.
https://www.mangago.me/read-manga/shounen_no_kyoukai/
Not sure if anyone would like this (bit dark) but it's a good example of all this happening :)

Fated mates mean nothing here lol
Typically to separate from a fated mate they undergo surgery, mc just brushed him off like it was nothing (/TДT)/
Babies are always a saving grace tho (づ ̄ ³ ̄)づ