According to the Latter Day Saints handbook "Sexual relations are proper only between a man and a woman who are legally and lawfully wedded as husband and wife. Any other sexual relations, including those between persons of the same gender, are sinful and undermine the divinely created institution of the family. The Church accordingly affirms defining marriage as the legal and lawful union between a man and a woman."
All photos by Neil DaCosta. You can se more of his work here, and more Mormon Missionary Positions here