My definition of that word seems to be different than yours. My husband is my soulmate, but not because he’s the only source of love in my life. I have another male life partner as well as a girlfriend. Our lives have had a lot of ups and downs and he hasn’t always brought me happiness, but that doesn’t change his status as my soulmate.
In fact, one can have many soulmates. My mother is another one of mine also. Here’s the definition of that word that I subscribe to:
Soulmates: different souls that we encounter on our path that are cut from the same “energetic cloth” as us and are sent to help awaken and challenge us so we can become the best versions of ourselves.