Terrible low self esteem

Alexandra
For the past two months my boyfriend has been in the other part of the state for harvest and he'll be back this weekend; there are other reasons as well but that besides the point. Lately I have been having very low self esteem. I have always struggled with this and it is due to what I have experienced with my own mother and what I have dealt with, with other guys. It'll be a year this fall and I can honestly say he is the best guy I have ever been with and the sex is amazing. He is very considerate and passionate. However I know I'm not what he prefers. I'm not obese but I'm not a stick either, I have a tummy. I have been working out but it takes time. 
Also I'm black, I'm my honest opinion we're the least desired of all women; I have no idea how he's still with me. 
I want to have sex with him but I'm embarrassed and ashamed of myself, to the point where I don't know if I want him to touch me... I hate feeling like this and I don't want to lose him because I can't love myself... How do I get over this?