Responses
I didn't remember that correctly, it wasn't Edea who said it, here
http://www.mangago.zone/read-manga/witch_hunter/an/en-manga/witch-hunter/105/1/pg-1/
From ch 105 they reveal that Tasha is Edea's reincarnation, but it's probably best o read the few ch before it too.
I don't think they are the same people
http://witchhunter.wikia.com/wiki/West
http://witchhunter.wikia.com/wiki/Edea_Florence
Because Tasha is Edea's reincarnation, they're essentially falling in love with themselves. Because that's basically a single soul falling in love with itself.