You may need grief counseling. You may be experiencing survivor guilt ("What right do I have to enjoy a dating relationship when he will never have that chance?") But in any event, what you need to come to understand is that while you may have loved your boyfriend, intensely, and while you may never forget him, he was not the love of your short life. Like most people, you will have several more dating relationships and several more love relationships, and perhaps marriage. This would be the case whether or not your first boyfriend died.
Best of luck.