John Stott has written a lot of books for Christians. He has also written a booklet on Same Sex Partnership. That booklet is available for free online!
From the back cover here’s the book’s description:
Many people think that homosexuality is a Christian option and churches are divided on the issue. John Stott surveys the contemporary arguments supporting monogamous homosexual relationships and tests them against Scripture. He explains clearly, yet with compassion, why same-sex partnerships are less than God intends for human intimacy. At the same time he calls the church to reach out to all with Christ’s love.
You can access it by clicking HERE. It is in Html format as a webpage.