As a female who has extra curves and a belly at this point in time.
I recommend you 1)start watching the chubby and or bww porn (i mean if you watch porn

)The more you watch it the less offensive fat will become to you. the more you will realize that sexy comes in all shapes. You don't have to get a boner or get off to it. you just have to watch it and become familiar with different body types 2) start looking around at couples and random people picture what they would look like having sex 3) take a careful look at yourself and figure out what your fears are and why you feel fat girls aren't good enough for you sexually. 4) don't get intimate with females till you feel you can look past any extra giggle they have.
I am not going to say don't date thick girls because you could end up missing out on a great relationship.. but i will say step back a little and work it out before you hurt someone self confidence and esteem..body put downs are very hard to bounce back from. Being told you are undesirable is heartbreaking.Men have many fears when it comes to sex but so do women and being rejected based on body is a fear that is shared by both sexes. Why do you think most females want to have sex with the light off.
Why do you choose these ladies? There must be attraction if you are wanting to fuck them yes? or no?