If a Kohen has a relationship with a non-Jewish woman, does he lose his status as a Kohen?
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A male Kohen who was not born as a Chalal (through an illicit relationship) can never lose his status of Kohen. However, the Mishnah tells us (Bechoros 45b) that a Kohen who marries women that are prohibited to him is not allowed to perform Avodah until he sends them away and swears never to have anything to do with them again.
M. Kornfeld