i have this weird phobia, and i want to get over it, but i'm not sure how..

i'm afraid to give oral sex or have any kind of sex with a woman that has slept with another man. it's tough to admit. i WANT to sleep with women i know who aren't virgins... but i have a part of me that doesn't want to either...

i'm not with a girl or anything right now, but i just want to get over it, just incase i end up with a nice girlfriend that has had sex before. i'm not sure what i can do to get over it, and i'm not sure why it disgusts me..

please help me figure out why it disgusts me and give me pointers on what i can do to get over it.