To be honest with you, in highschool and college I was rather promiscuous. I had fallen away from God, and did a lot of things I regret. I can honestly tell you, when my husband and I are together, it's a million times better than it ever was with guys I had no feelings for. In terms of the relationship, I would say it's pretty important, not the sex itself, but rather the emotions and feelings shared while making love. It's one of those things I think just makes your relationship even more special. It's so much easier to open up and talk to one another when you are able to share each other's body. Sex definately isn't the most important part of the relationship, but it definately gives it something wonderful. Think of it like frosting on the cake. You don't have to have frosting to have a great cake, but frosting is one heck of a good compliment to it!
Just take it from someone who's fallen down the path of promiscuity...while sex is fun and it feels great, when you throw your body away on just anyone, you end up feeling horrible. You feel guilty, and disgusting, and worthless, and soon all you feel you have worth anything is your sexuality. But when you meet the right person, and you share that love together, it's completely different. I wish I would have saved myself, because honestly, sex isn't worth it unless it's with your spouse.