There are plenty more fish in the sea
I felt similar to that when I was 20. When you meet someone (yes I said "when"), be very careful not to get sucked up in the moment and marry the first one you meet....UNLESS you are sure about it. I met a girl when I was about 20 and from the moment I met her, all kinds of emotionally unstable flags went up in my head about her. I ignored the signs and ended up marrying her about 3 years later. She was my first GF so I was in for a bumpy ride on the relationship roller coaster. I was so afraid of being alone that I put up with years of craziness and such.
I"ll stop my ramble but my main point was to make sure you are 100% committed before making a decision about marriage.
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When u hit the walls of sanity, u have no-where to go....