Revers cowgirl.. Help.😭

So my boyfriend of two years was really excited to do revers cowgirl.. We tried it the other day and.. Well.. No. It was horrible and I had no idea what I was doing and he went soft.. HE WENT SOFT! I have never made him go soft! I wanted to cry.. How does it work? How far do you sit up his thighs? Do you go up and down or grind? He is great though because at the end we just laughed about it and he told me it was okay. However he wants to keep trying it..