I agree with you ,I think it wasn't sexy at all, I was afraid for har when he did that I was afraid she will get heart she is pregnant and he took drugs, but marc deserve to be boshed away. 
Thanks omhamdy, of course you are totally right. This is exactly what happened. That's why I don't think it's sexy.
But I think I understand Alicat. Her approach is from Marc's point of view in relation to Kay.
In the comments they said something like that: Marc wanted to try out with Bettina what he was experiencing with Kai.
When I look at that scene, it's difficult for me to see it that way because of how he is treating his pregnant wife (with drugs in his blood!).
But, from Marc's point of view, I agree with Alicat: Marc seems comfortable and experienced with this. It tells us something about his sexual relationship with kai, it makes it easy to imagine how they "do it".
So if I try to imagine this scene with Kay instead of Bettina, it is kind of sexy.