Sounds like you have worries over your current relationship.....probably stemming from low self-esteem, or actual doubts about your relationship.

Have you done anything lately, which would cause you to feel guilty, or that you don't 'deserve' your boyfriend, or that you are not worthy of his love?..(gained weight, forgot something he told you about...etc)
Does he treat you wonderfully, and you wonder how you got 'so lucky' to have a guy like him?
Has he given you any inclination that he's not 'happy' with you, or your relationship?
Do you have feelings of insecurity, maybe 'left-over' from a previous relationship?
Did you meet his 'ex', or see a picture of her, and you think she's 'prettier' than yourself, or that she's 'better' than you somehow?
Do you feel you've found true love, and you worry it won't last?
Are you 'ready to commit' to a lifetime with this man, but you fear he doesn't feel the same?

Affairs of the heart is a 'tricky' subject. True and lasting love is an elusive creature. Sometimes when we actually find it, we're afraid it's either not real, or that it won't last. Yes, we are emotional beings, and we 'wear our hearts on our sleeves'...but that's part of what makes us human. The ability to feel and express emotion.
Have faith in yourself, and your self worth. Take each day as it comes, and accept love when you find it.

Hope this helps.
Hugs,
J