I have read in a book, "Eat, Love, Pray" (the author escapes me at the moment)... that your soulmate isn't necessarily the one you will spend your life with. That they are the person who shows you who you really are, kicks you in the butt, shakes your life up and then moves on... Living with them is too hard, as they are a mirror and sometimes we don't like the reflection they show us about ourselves.
Keeping her in your life will have its benefits, however, I don't know if "getting together" will. You are in control of where you go and how you think. I would be really cautious if she is currently with someone else and is telling you that you all have a future. Seems like she is just creating a safety net for herself, not a security blanket for you.
A quote to think about:
"True Love isn't finding the right person, it is building the right relationship."
Not sure who wrote it, but it makes perfect sense to me.