...what if my girlfriends dump me for being too boring?

Sounds like abuse to me. He gets off by hurting you, and being slapped in the face is very psychologically degrading. He gets off on that too.

You deserve better. He sounds like he will only get worse. People like that do. After a while, he will have to hurt or degrade you more to get off.

Don't let him do that to you. Try to find someone else. That is not love, or even good sex. Being slapped in the face is clearly sadistic. He is trying to break your spirit. He does not love you. He just wants power over another person.

You are Better than that. I hope you will move on and find someone that treats you better.
Good luck

what if she wants to be spanked, if she is Bad?

what if she wants to do the spanking

But if its the only thing that makes him to dig harder for you to be satisfied, why worry, let him but when he finish lough together

Maybe search for any old blog postings from David Caradine? I think he had a few creative ideas

Creative ideas ?

I like my partner very much, but he likes to slap me on the face. It arouses him. During sex, I let him to do as it makes its dick hard.
But I dont like to be slapped, what should I do ?

It might seem silly but you need to have a serious talk with him

If you don't like this, then you need to have a serious conversation and be prepared for the possible consequences.

Join fight club.