Welcome sister Rachel84.

What if you thought you had found your soulmate...and then he decided to go back to being a sunni again and when you tried to pull him back, he ignored you and went off and married another sunni?
And yes this did actually happen to me!
Perhaps he didn't have firm reasons when he left Sunni at the first time.
I suppose God saved you from him.
Btw, does Qur'an ever mention about "soul mate"?
It mentions about spouse, but it seems I haven't found verse that tells a person has a soul mate.
But if there is soul mate for each of us, I think it is a wonderful blessing from God.
Peace.