Your soulmate isn't someone who just exists out there and you magically discover. Your soulmate is built and discovered over the course of a relationship. My fiance is my soulmate, but there were choices we could have made over the course of our friendship then romance that could have led to neither of us feeling this level of profound spiritual love. Your soulmate is the person who you show your true self to, who reciprocally shows their true deepest self back. They become your soulmate when both of you together recognise each other as such. If one person thinks the other is a soulmate and the other doesn't, it's not a soulmate yet.

Someone might become your soulmate only after you know them for a long time. Once they are your soulmate, then even if you met the perfect stranger, they can't replace your soulmate because they don't have that history of deep sharing with you.