Any sex outside a male and female marriage is a sin. http://bible.com/100/lev.18.22.nasb You shall not lie with a male as one lies with a female; it is an abomination. http://bible.com/100/rom.1.26-27.nasb For this reason God gave them over to degrading passions; for their women exchanged the natural function for that which is unnatural, and in the same way also the men abandoned the natural function of the woman and burned in their desire toward one another, men with men committing indecent acts and receiving in their own persons the due penalty of their error. The are more, but it's not needed.