I am living testimony against getting married young just because it feels "right" or "okay."
When you are young, the course of events feels huge. Short periods of intense love and feeling seem endless, and permanent. But, as I learned at 22, when you marry your college friend with doubts in the picture, it can easily mean disaster.
The Pain of Divorce is worse than a Stopped Engagement
My girlfriend, then wife, and I were great friends with a wonderful network of close friends. Our families were close, and I absolutely loved her whole family. It seemed at the time, that even though there were really deep issues between us, the intensity of our relating could make it all work.
My wife had many doubts about me being the right one for her. Instead of saying no, when I asked her to marry me, she said yes, and the doubts grew. They grew until she finally said, 10 months after we were married, that she thought it was a mistake to get married. Believe me, after a huge wedding, and all the expectations, the pain of divorce was much worse than the pain would have been if she had stopped the engagement.
Don't Stay With Someone Just Because They Will Be Sad If You Leave
You should never stay with someone just because they will be sad if you leave. Love works when both partners are looking out for themselves first and foremost. If you are staying with this guy to take care of his feelings, you will definitely grow to resent him and feel like you are sacrificing yourself for some idea of the relationship.
So, please, for you, for him, take care of yourself now. Trust your doubts. They are "undoubtedly" real reservations. You have to move beyond his sadness to what it is you are really feeling.
Talk to him honestly about it. Talk to your parents, your friends, your church leader, your therapist. Mostly, though, you will be talking to YOU about what YOU really need and want.
You may find that as the doubts come out that they will feel less important (you HAVE been with him quite a while, was it just because you like him and don't want to hurt him?) Or, have you been with him because the real love is there, and there are issues you need to work on together? But examine these doubts...real love will wait for the doubts to be resolved.