I don’t understand. If a woman takes it up the butt that’s straight sex meaning it’s ok but if a man does it’s a sin. Please explain.
God designed sexuality to be between a married man and his wife for a reason. That reason? Only men and women can make children together, something two men or two women together can’t do.
Biologically speaking, sex is the procedure that is implemented to procreate. Any other act is not sex, but stimulation of sexual organs and mimicry.
As an extreme example, when a man has a “wetdream”, is that sex? Of course not, though the events might be similar.