MickeyTheBrick's advice is very sound indeed.
You need to talk over your low esteem issues with your boyfriend. If you are close enough for physical intimacy, you are close enough for emotional intimacy. Explain about your past, and tell him you need some reassurance about how much you mean to him.
You also need to address these issues yourself.
When you get up in the morning, look in the mirror and say out loud, looking yourself in the eyes -
"I am a good person. I am a valuable person. I am worth loving and giving love."
Say it three times, and mean it. Do it evey day, and repeat it under your breath at odd times, and you will start to beleve it.
If you need support, come on here, there are loads of people who will offer you constructive support based on personal experience - don;t let Buenochicho's somewhat brusque approach put you off.