Wow, I haven’t heard of this before.
My thoughts are that I agree that you have obviously desensitized yourself from this (rough?) bed humping.
However, what about the psychological part of this?
You have the opportunity to switch from bed humping to a real girl, rubbing and sucking your dick. A real girl with a real vagina who wants to fuck you. That should get your dick hard just from the thought of it!
I assume you are young? If that is the case, and ED isn’t an issue, then an erection isn’t just about friction. It’s about what is going on in your head.
Sorry I can’t offer an instant solution, but think about what you consider erotic and what kind of thoughts translate to physical arousal for you.
Part of it may just be performance anxiety with your girl. If you like the thoughts of being naked with her and enjoying her body, then try going slow and touching and snuggling without the anticipation of sex. Let the erotic thoughts and excitement fill your mind, not just thoughts of how many RPM’s it takes to maintain an erection. Good luck.