I’m a girl and I’m 17 and I’ve never cummed before.. And everytime I’m with my bf and we’re doing things to get me going my legs start shaking and I don’t know why should I let him continue ?

Okay, well, good news! It seems you have a problem easily solved. Legs shaking is exactly what is supposed to happen because that’s when the awesome stuff starts so yes you need to let him keep going… That’s how you orgasm… You keep going.