Congratulations to you and your future wife, bro! That's exciting news.

As for what marriage means, as Victoria mentioned, you don't need it to know who you want to be with, but I don't think that's necessarily the point. It's two people telling each other definitively who they want to spend their lives with. Marriage is a connection that bonds you to another human being, both legally and spiritually. How I view it is, you aren't whole until you find somebody (or in some instance, something,) that fills every void in your life, and when you find that person, it just makes sense to seal the bond.