And murder.  And incest.  And lying.  And stealing.  And divorce.  And so on.

That doesn't mean any of those things are "a part" of the religion known as Christianity.  It just means it happened.

"Jesus replied, “Moses permitted you to divorce your wives because your hearts were hard. But it was not this way from the beginning."

"‘For this reason a man will leave his father and mother and be united to his wife, and the two will become one flesh"

Matthew 19: verses 8 and 4.