Soul mate? What's that?

Who is a soul mate? Or rather what is a soul mate? I don’t understand the concept of soul mate. It literally means ‘someone for whom you have deep affinity.’ Affinity means ‘a deep liking for someone.’ So then one could have a deep affinity for more than one person right? So does that mean one can have more that one soul mate? In that case, what is so mystical about finding one’s soul mate? Why do people race after this thing called soul mate? Or is it just another chase for something that takes us away from the brutality of our reality? Most people marry the person for whom they have a deep affinity and the remaining lot develop that affinity for whatever reason after they marry. But then again a soul mate may not necessarily be someone you’re in love with. It could be a friend or just some person you know. Then why the term soul mate? The concept of soul mate is very vague to me. There is nothing concrete or definite about it. I think it’s just a source of deviating our mundane lives by introducing a search for something we don’t really understand or have misinterpreted. How can one search for something that one does not comprehend? The end result of which only leads to unhappiness and dissatisfaction. The search or chase for a soul mate in my opinion is insatiable because for us humans it would be difficult to choose the person with whom we would share a deep affinity. It is simply difficult for us to decipher. It is excitingly surprising that one word, soul mate, can start a chain reaction of such profound and complex thoughts. Would anyone have the answer to my queries? It would be nice to have some clarity.