Was there a sex scene in
Foundation's Edge? I remember Trevize and Pelorat were both interested in Bliss, but I don't remember anything happening on the page. (Pelorat and Bliss, of course, become a couple.)
There are a couple of sex scenes in
Foundation and Earth -- Trevize sleeps with a government official on Comporellon, and then he sleeps with one of the natives on Alpha and picks up an STD.
The most memorable sex scene in Asimov may be Lije Baley and Gladia in
The Robots of Dawn.
Two thorough articles on Asimov the creep, for those unaware of his history: