Im insecure about my relationship! help me!

ok so i have been in a relationship with the perfect guy for a year and 4 months. i have been very insecure for a couple months now. my bf has told me that he preferred puerto rican and african american women over any other race. i am mixed with white, african american, and native american. everytime i see a good looking puerto rican or african american girl walk past i make sure that my boyfriend doesnt look at them and if he turns his head a little bit i think he wants her or something. i get jealous when there are half naked girls in pictures or movies and make hime turn away or cover his eyes. yeah i guess im really bad but i cant help it. he used to be a big flirt but since i have been in this relationship he has never given me a reason to think he is cheating. i think i am good looking most of the time. i have my own insecurities. ive never been cheated on and he my first really serious relationship. im so tired of worrying about what he is doing and that he will leave me for a better looking girl. how can i stop being so insecure? i am afraid of losing this relationship and i feel that if i carry this on then it will end. please help me!