I honestly don't think that everyone has a soulmate. Also, not everyone even meets their soulmate, due to many circumstances, such as being reincarnated at different times, and so on.
The more spiritually advanced we become, the more clear these matters are. But if you're not happy in your relationship, maybe talk to her, tell her there is someone else interested in you... open communication is more important than many people understand.
As for "twin flame", this is new-age terminology, trying to replace soul mate. I've read where they state a soulmate is someone you are romantically involved with before meeting your "twin flame". A twin flame is someone similar to you, this could even be friends, its like the term kindred spirit. A soul mate is not like a "twin flame", because romantic partners usually balance us, and are not a "twin" in any way. Thus, I disagree with this new-age terminology. A soulmate is the highest romantic partnership, not "twin flame".