If I could, I would find out who I am going to marry. Not when. Not where. Just who. I wouldn't find the person and throw myself at them, act like I don't care in fights because I know I'll be stuck with them, or tell them I know they are going to marry me, but I would find out who. There are so many advantages to finding out, and very few disadvantages. If I did find out who I am going to marry, then I could relax in other relationships and not take it too seriously, I wouldn't have to hold back my heart dating them, and I would avoid getting my heart broken. 
Dating is sometimes scary. If you are interested in a relationship, then you search for someone to share that with. If you are interested in a certain someone, then you attempt to get them to like you as well. Once you both decide you want to see each other and pursue a relationship, you start going on dates. However, knowing you are not going to marry them, simply provides ease. No falling too fast or too far, no getting your hopes up, just all fun. Feeling good about yourself and being happy is the biggest perk of a relationship, and that's what you can have knowing they are not the one.
A piece of advice lots of adults will give a dating teen, is you have to hold a part of your heart back. For if not, you will get too attached and be broken inside because the majority of relationships you have don't work out. Only the one match for you will. Therefore, finding out who you will marry means you don't have to hold back a part of your heart. You can love with everything you have and fall head over heels in love. And if you are going on dates with someone that you know you are not going to marry, then holding back a part of your heart isn't a problem, considering it would be your choice to go on with getting your heart broken.
My opinion is that every single person to walk this earth has or will have their heart broken. It’s like some assurance test to prove that you are human maybe. But in all seriousness, this shattering feeling is simply terrifying. You can do absolutely nothing to avoid it; there is not even a cure. I have recently experienced this feeling, so I can relay it quite easily. Who would want to shake because they are crying so hard, gasp for air because they can’t stop crying, cause their eyelids to become swollen from all the tears, lay awake at night replaying every word of the break up, and so many more depressing aspects? Unless you fancy these ideas, no one would I know of anyway. If I could find out, “Hey, you’re going to marry Hunter Hayes,” then I would avoid any heartbreak of dating someone else. In my book, that is definitely a win-win situation.
Finding out who you are going to marry doesn’t ruin anything or give away a secret. It doesn’t mean go find them this minute and get married either. As long as you don’t change your life to waiting around for this person or waiting for your wedding day, only positive effects could come from this. The ability to avoid brokenness, loving with your whole heart, and not stressing out about relationships only to temporary cause happiness would be absolutely outstanding.