Correct spelling, explanation: separator is a noun made from the verb separate, which is borrowed from Latin separare. Due to that, nothing is changed in the internal structure of the word, so the current version should be as similar to the Latin original as possible, making separator the only correct option.

Definition of separator:
Noun
1. A thing that separates something into two or more elements, often a machine
The milk is separated from the cream in a special separator.
Commas are the only proper separators between e-mail addresses.

Incorrect spelling, explanation: the pronunciation may be misleading, but considering the fact that the word comes from Latin separare, there is absolutely no reason to change the original a to e. Seperator is the incorrect form because it simply has no linguistic reason to differ from the Latin base word.

Incorrect spelling

Incorrect spelling

Incorrect spelling