I don't know much about this film but I remember that a woman drops her shopping outside a man's apartment and the man invites her in. The woman keeps going to see this man and the woman's husband asks someone to watch her. I think in the end the husband kills the man who the woman is having an affair with.
Can you please help me work out what this movie could be!
Thanks

I think it is "unfaithful" with Diane Lane; she drops her bags of groceries outside a man's apartment and they end up having an affair - her husband is played by Richard Gere.

Probably http://en.wikipedia.org/wiki/Unfaithful_(film)

So close...