Just a midnight thought

So I've been thinking what does make you think that you want to spend your life with someone.Its just that so many people around me are getting married and I just don't understand how can you spend (or at least try to) the rest of your life with just that person.When do you know for sure that you're reading to give your time and strength (...) To only That person? How do you describe that feeling?

I know it's a very personal matter...so I apologise for my rudeness to ask this.
Maybe it's cause I lack age that I don't comprehend how can i see ,and live my life with that one person EVERY DAY for the rest of my life? I'm 100% that I'll get tiered...I guess marriage or commitment is much harder than I thought. ╮(￣▽￣)╭ I hope at least someone gives me an answer( I can just imagine everyone going "what the heck with this topic...(￣∇￣"))
Anyway, thank you for reading this (and it's ok if you don't reply)