Duck and bunny,
That was enjoyable and at times hot--somewhat more the first half, because of the teasing.
On the positive side, its plot is a bit unusual; you managed some surprises in a very cliche'd area.
I guess one problem area was Steffi's cruely and our hero's reaction to it. He loses his erection, then has to get back into it. I wonder if he isn't a bit too involved with the husband and his 'plight,' engineered though it is.
I did like our hero's effort to turn the tables a bit, withold, fuck her ass (almost) and so on.
I think the problem here is that Steffi is rather uncomplicated, with this ravenous, 'put your cock in my cunt' approach. A little complexity would help. A little less 'having her way,' at every turn. Possibly some area of vulnerability? I suppose she's just too much the superbitch to be entirely attractive and hot for me. Apart from literature, real life persons have various facets.
Since you're looking for something a little fresh, that's something going for you. Some more characterization would be nice, and some indirectness, teasing and delay, in the action. The start with the blow job was a step in that direction.