At 20 you have not lived, nor have you done the things all 20 year old are doing, like dating, partying, being crazy, and loving life to the fullest. You have a lifetime ahead of you to get married, and the fact that you questioning your relationship, should be enough to send warning bells out. You cannot possibly love him, as much as you think you do, if you are unsure that it is enough to sustain your relationship
My advice to you would, break off your engagement and be honest with your fiancee. If your relationship is based on trust, honesty and integrity he will understand, and perhaps even allow you the space to find out what it is you really want. Dont hand onto him, from fear that you wont find better, as that would be selfish.
RE: raining
The glass is half empty,yet full. Dpends on how you measure the glass? when its empty or half full...............