Sex is a gift that God has given us; however, sex is meant to be within a marriage, a marriage between a man and woman specifically. Sex was never designed to be shared with multiple partners. God has designed us to be extremely relational beings. Sex is supposed to create a deep spiritual, physical, and emotional connection. Sex is a representation of the husband and wife being one just as Christ and the church are one. Therefore, that is why sex is only supposed to be shared with one person: your husband, or your wife.
God is my Heavenly Father. Just as my earthly father creates rules or regulations to protect me from hurt or danger, my Heavenly Father does the same. Abstinence is one of these rules that was made to protect. God designed sex to be within a marriage to protect His children. God's ultimate design or plan is not for people to have children outside of the marriage or to be pregnant as a teenager. God's desire is also not for us to be heartbroken. An analogy that always made sense to me is the analogy of a piece of tape stuck to an arm. If I placed a piece of tape on your arm then removed the tape, there would be pieces of hair and skin left on the tape. If I then placed the tape on someone else's arm, your skin and hair doesn't go away; the other person's is just added. Eventually over time, the tape will have so many different people's hair and skin that it will be unable to stick to anyone's arm. Just like the tape, anytime a person has sex with someone, there will be some connection left, and that is guaranteed. Every time that person tries to have sex with another partner, there will be less connection than with the first partner, because the person will still be connected to the first partner.
For this to fully make sense, I feel that our society's value of marriage must increase. Marriage is not just a promise between the couple, but more importantly a promise between the couple and God. After understanding this, it is logical that the deepest connection that could be shared on earth is meant to be experienced within the most important relationship that could be shared on earth.