I think too many people today get married for the wrong reasons. However, I think you have to be careful and not get too involved in other people's business, especially friends. If you know something she doesn't, then you may want to approach her as a friend and let your feelings be known. The decision ultimately has to be hers and you need to support it, whatever it is.
I knew at 15 that I would marry my husband some day. We dated for 5 years all through the high school days and never felt like we lost anything. Never lived together, never would have considered it (but that's just us), got married at 20 and have been married for 21+ years, together for 26. I found out later my sister-n-law said it would never last. I think a lot of people felt that way, especially my parents. They had other plans for me, but ultimately left it up to me. They now think he's the best thing since sliced bread and jokingly ask me how I landed someone so wonderful.
We got married on $5 an hour while I was in college. We didn't miss out on anything, we just did it together. I did the sorority thing, finished college, he finished college, we have since then earned 2 more degrees and have 2 wonderful teenage boys. We did wait to have children because we wanted to spend time together just the 2 of us. We travelled, got better jobs, and then had our first son 5 years later. Our second son is physically disabled and that just adds another whole new dimension to a relationship.
Marriage is a lot of hard work. Big ups and downs. But you have to remember why you married the person in the first place. I think the secret is to be friends, learn to forgive and put all pride aside. Its not important to win at the cost of your family.