Because we don't care if we take the lord's name in vain.

Means of expressing yourself. Part of language. You do not affirm anything by saying them. You could say something else like eg. "yellow dolphin" with about same effect - if it was part of social convention.

Its not easy to stop to say that kind of word because its not easy to move on even you decided to be atheist like me iam ten years cristian but iam atheist i can say that words cause that kind of word i practiced in ten years of my cristian life

Hell, why is "god" being used, too? We shouldn't even assume that these words have functional merit to begin with. I usually break words down to the most tangible and deliberate posits possible:

Soul Mate = The assumption that out of all the people in the world, there is one that is absolutely compatible in every way and it is mandated by a supernatural deity/force for you and that individual to end up together even if it is only in the afterlife. What if it's an alien?

On a secular and more pragmatic level what could "soul mates" mean? The notion that there is one person on this planet that is most compatible with you AND you are most compatible with them. This takes on a great heap of assumptions that go far beyond your question and I do not have the brain power and/or desire/patience to sit here and elaborate upon. I think we can all gauge at the impracticality that even a secular version of "soul mates" implies.