I really don't think there's any such thing as soulmates. I think the whole idea is just a reflection of this world's attitude that "you are who are and if people don't like that they can kiss you...
Shouldn't bother what? I'm not saying we're all 'destined' to be with someone but that there may be one person above all other people that you get along with.
Maybe it's different for sisters. Or maybe I'm just weird. If you truly believe that you have found your soulmate then I'm very happy for you and I wish you all the best in your future relationship. I just know that recently I've been agonizing over how I'm going to find a sister who I like and who even remotely likes me. Compound that with the fact that I am not fiscally, spiritually, or emotionally ready to get married and I am quite distressed about the whole idea. The prospect of having to worry about whether the other person is my "soulmate" or not is too disheartening for me to even deal with, so I choose not to believe in soulmates.
I can totally see how there are just so many things to deal with that it really is just another added worry to think about soulmates. On the other hand, it's a really nice thought if you think you have found your soul mate. You can just look at that person and be like "wow..despite the differences and all the work we still have to do to make this work, we're perfect for one another."