Need advice help

So my boyfriend has really had anxiety and it’s hard for him to keep his nails from his mouth!! He always ends up hitting off his WHOLE NAIL when he gets anxious. He tried the nail polish which helps for bitting your nails but they’re just not strong enough, idk what else could help him because he always gets insecure when he sees his nails and hide them. Imagine hiding ur nails everyday!!!! Pls help what should i tell him

This is right now but it’s nothing compared to what he has done before (at least there’s actually nail on his finger and not just flesh)