AMITY, ETERNITY, INFINITY
The three letters AEI stand for "AMITY, ETERNITY, INFINITY" and signify everlasting LOVE:
"THE LOVE that I have for You will last through all ETERNITY and into INFINITY, or I will LOVE You FOREVER and Ever "
This was a popular type of acrostic love tokens among the Victorians, probably borrowed from the ancient Greeks.
The initials can be found on almost all jewellery medium known to exist at the time, indicating that it was a very popular way to tell someone that they were cared on.