"Soul Mates" as a term probably means something different to everyone who uses it. When I met my partner he told me he was looking for a soul-mate. It was some time after that I realised that he's an atheist.
I said,"What's with looking for a soul-mate when you don't even believe in souls."
To which he replied," If I had a soul baby you'd be it."
I, on the other hand do believe in souls and for me a soul-mate is just another soul who connects with you on a very deep level. I think we can have many over the course of a lifetime.