I've been through the same thing. *hugs*
The best thing is to get your esteem up. I know its tough to think you're worthy but you are. You deserve happiness and joy and love. Everyone does.
Never question why your bf is with you. He's with you because he wants to be When you do question it, it causes you to overthink and be jealous of females in his life (be it work, friends, etc.)
I know what you mean by meeting someone who's changed your life...filled in what was missing and the fear of losing it. Try to think positively and know that you can control your emotions and that your bf loves you...for who you are.
I wish you luck.