i can tell you from a societal and medical point of views why sex before marriage should be avoided.
in this society, sex before marriage and having multiple sexual partners is considered the 'norm'. this has lead to many children being conceived and mostly raised by single mothers. it is rough life for single woman to work, take care of the kids by herself. and a lot of these children don't know who the father is or have a relationship with their fathers. children don't have a stable environment when mom is out dating different guys with these guys walking in and out of the children's lives, some are mistreated by the guys mom is having sex with. i have taken care of one too many kids who were sexually abused by mom's boyfriends. the impact of people who have sex before marriage and with multiple partners resulting in conception of children is enormous on society and the impact is generational. the best environment for children to grow up is when you have a stable home with mom and dad in a good marriage.
there is also the medical reasons - the various STD's that's out there and will be cropping up in the future. the medical costs of treating STD is enormous. Have you heard of anyone being all excited and feeling good about being diagnosed with HIV, HPV, etc. If we all had sex only after marriage, the prevalence of STD would be very low to actually none.
then there is the emotional and psychological reasons. we are human beings. we have emotions, feelings, memories. you have memories of the person you have been with. sex is the closest you can be physically with another person. if that relationship ends, surely it cannot be good for the pscyhe/soul. so, sex before marriage can hurt at different levels.
at the purely sensual point of view, sex in a loving committed relationship is the best and highest, ultimate form of pleasure. hey, God who created us knows what is best for us!