Start by eating your own cum out of her pussy You won't really want to the first couple of times, but ask her to encourage you and tell you how much she likes it. If she tells you that it is really important to her that you eat another man's cum from her pussy then you will find it easier to do this just for her. And after a while you will probably learn to love the taste of semen. When you get comfortable doing it after fucking her it will be so much easier to do it right after she has fucked her lover and you still have an erection. When she sees you with a hard-on and enjoying licking another man's spunk from her cunt she will know that you love her enough to do anything for her.