When having sex, my girl can't cum unless she is penetrated hard and fast AND I am stimulating her clit at the same time. I am not very coordinated, so it takes a lot of concentration to do the both at the same time. Also, the concentration on movements sometimes causes me to get soft, which makes her frustrated (close to tears). I have asked her to stimulate her clit by herself, but just like when I asked her to masturbate for me, she says "it just doesn't work" when she does it solo. What do?