Bro, I don't even know where to start...
When the relationship is good, she can make you feel like no one else can...and at moments you feel like you're glimpsing a peace of heaven in this life.
If you're reserved, like I am, then you have someone to shower with love and affection of physical, mental, emotional, spiritual, and creative natures...who not only accepts it, but reciprocates everything back to you.
If it works out, then this is a life long thing..,and if it 'fits' (so to speak), you actually make each other better people. She'll be a compliment to you (and you to her) in ways, places, and things that you wouldn't do or be apart.
...something like that...in my experience...but then, I'm still single, so maybe you shouldn't listen to me... ^_~ (at least from a long-term credential stand-point)