Dear Father Jim,
I think I may have found my soul mate, how do I know for sure?
Congratulations on having such a powerful relationship! I'm happy to hear when others are happy!
In terms of your short question though, I had to smile. While I can understand your looking for guidance - how would a priest, who's never known you be able to tell you if you found a soul mate???
Part of the beautiful and mysterious part of a loving relationship is the idea of living with that "question." - You love someone, they love you - you give more and more of yourselves and, if called to marriage, you take the plunge where you promise to spend your lives helping each other to get to heaven. That's the core of what marriage is about and that you find your joy in life, your fulfillment in doing that.
There's not a "billboard" moment for this - it's something special, unique, precious for every person, for their own individual love stories. Unfortunately God doesn't send us guarantees in these situatlions (mostly because he's dealing with us, free- human beings, who sometimes make bad choices and mess things up --- ask Adam and Eve... : )
My response would simply be another question, if you think you've found your soul mate, what's holding you back?
Father Jim