There really isn’t any way to explicitly know. Maybe that’s not even a possibility and one simply has to believe they have, for better or worse.

All couples starting in a relationship have the potential to be each other's soul mates. They share intimacy and trust. Sometimes that is not enough, and sometimes it is all that is needed to thrive and flourish together. Love can only grow if it is battle-tested and hardened by life, time, and situations. Are you willing to forgive a fault and still love them? Is he/she willing to forgive you? Is your relationship with each other the most crucial thing in your lives? It takes work, tears, and heartache over many years to know for sure.
It's something you build together while living your lives and making a family .

There really is no “one person”. There’s plenty of people that could feel like your person. Not everyone is for you but there are plenty of people that are.. not just one.

No way to know for sure. Even if you love everything about them and always will, they might change and lose feelings for you after some time.

No, and that's the fun thing. There could be many people out there for you :)

If they are there for you..

you life should improve with the person. Otherwise what's the point?

Nothing is for sure. You make your best decision and hope for the best.

If you are still asking, perhaps you have not.

Yes, you will find out on your own

Only God Knows that answer.

Yes. Wait for 50 years...

if sex 6 times a day -- then yes