years ago, i became a church member.. until now i dont know why we need to be baptize? 

1 Corinthians 6:18-20
"Flee from sexual immortality. All other sins a man commits are outside his body, but he who sins sexually sins against his own body. Do you not know that your body is a temple of the Holy Spirit, who is in you, whom you have received from God? You are not your own; you were bought at a price. Therefore honor God with your body"

The thing that really stands out to me is the question Paul addresses to the church and essentially us as believers, "Do you not know that your body is a temple of the Holy Spirit? You were bought at a price." I would encourage your boyfriend to contemplate this through and see if his acts are glorifying God and God's temple or more himself and his own desires. 

i'm reading this book as well...Love it...but to tell the truth...i'm scared to finish it...because the things in there are so true... 

why is it a sin? where is scripture supporting this? 

yeah but what about guys? 

hey there....in response to your question...there is a book out that is called "Every young womans battle". It is a very good book and I would recommend every girl/woman to read it. It deals with having sexual integrity, and what to do to stay pure in your christian walk. I really hope you will read this book, it has helped me in many different ways. Good luck and God Bless.