I hold that they are both. There is that something special from the start but you continually grow closer. Michele was my soul-mate. Note that a person can have more than one. Just one at a time
I agree that you can have more than one (I've had 2, exactly 20 years apart).
I believe you get closer, but there has to be that lock-in from the start. Like with my first hubby and I...folks used to say we were so much alike it was scary. A soulmate truly knows you, even things that you don't know about yourself.
I've also seen couples who are divorcing after 30 years of marriage because they aren't one bit closer on day 10000 of marriage than they were on day 1. You can grow compatable, even love each other, but soulmates is something way different.
It's there or it ain't.
Personally, I won't settle for less, or think it can be made better, or that soulmates are not important. I did once, and it was the biggest mistake of my life.