Research shows out of everyone who is having sex, the least satisfied are unmarried people.*
The ones who had sex outside of marriage knew that even though it felt good during the act, that did not mean they felt good about themselves afterwards. The guilt, along with the anxious fear of being used, getting pregnant, or contracting disease, lowered the sexual satisfaction big time for those who were not married.
On the other hand, the same research shows that those who were happily married to a faithful partner had the highest reports of sexual enjoyment on both a physical and emotional level, and they were most likely to feel "satisfied," "loved," "thrilled," "wanted," and "taken care of."*
*Laumann and others, The Social Organization of Sexuality, tables 10.5 and 10.7, as quoted by Stanton in Why Marriage Matters, 41.

*Laumann and others, The Social Organization of Sexuality, tables 10.5 and 10.7, as quoted by Stanton in Why Marriage Matters, 41.