Suggest Treatment For Nits And Itching On Skin

Hi, I've had crabs for a few months now but I'm not sure if that means my boyfriend cheated on me or if I caught them from somewhere else. I already applied Permethrin cream once before and picked out whatever nits I could with my fingers. But now it seems like the crabs have come back. It's less itchy this time but they are definitely back. What should I do? Moreover, is this evidence that my partner is cheating on me? We have a healthy and (apparently) monogamous sex life. Please do advise me