There was a movie made in the 1940 or 1950 with the lead actor I
beleive William Powell (Icould be wrong)  He was tall anyway.  The
storyline was about how this married man was having an affair with his
daughter's girlfriend.
I remeber him sitting in his smoking chair in his home reading the
paper and saying something to his daughter.  I beleive somewhere
toward the end of the movie his daughter found out about the affair.

Hello.

I suspect that you're thinking of "Ten North Frederick" (1958)
starring Gary Cooper.

It was a 1950s black-and-white film about a man who has an affair with
his daughter's friend.

See:

"Gary Cooper plays Joe Chapin, a very successful man turning fifty years old
... he finds solace in the arms of his daughter's roommate, half his age.
...This is an over looked drama shot in black and white. Daughter Ann
is played by Diane Varsi and her roommate Kate is played by the lovely
Suzy Parker. Also in the cast are Stuart Whitman and Ray Sticklyn."
source: Internet Movie Database:
http://www.imdb.com/title/tt0052283/

"Ten North Frederick (1958) Cooper as a businessman goaded by
ambitious wife Geraldine Fitzgerald, ultimately finding true love with
a sympathetic young woman (Suzy Parker), but alienating his children.
Directed by Philip Dunne."
source:
Gary Cooper Filmography
http://themave.com/Cooper/filmog9.htm

"TEN NORTH FREDERICK  Gary Cooper plays the part of a reluctant 
politician, who is manipulated into politics by his domineering wife. 
... Eventually, as he becomes more and more miserable, he finds
himself turning to his college-age daughter's girlfriend"
source:
Google Groups
http://groups.google.com/groups?hl=en&lr=&c2coff=1&selm=33da619d.12716223%40news.airnet.net&prev=/groups%3Fq%3D%2B%2B%2522gary%2Bcooper%2522%2Bdaughter%2Baffair%26hl%3Den%26lr%3D%26c2coff%3D1%26selm%3D33da619d.12716223%2540news.airnet.net%26rnum%3D3


--------------
search strategy:
google groups: "daughter's girlfriend" movie
google: "ten north frederick" cooper

I hope "Ten North Frederick" is the movie that you had in mind. If for
any reason you feel that it's not, please let me know via the "request
clarification" feature. Thanks.

THNKS ever so much.  I have been looking for this movie for years!