Shopgirl

Bingo...

Ray Porter (Steve Martin) is a considerably older, suave, well-dressed, wealthy, divorced logician. Ray charms Mirabelle over the course of a few dates, one of which ends at his house. Mirabelle offers herself to him, and the morning after they have sex Ray tells her that he does not intend for their relationship to be serious due to his constant traveling between L.A. and Seattle.
Ray thinks of Mirabella as a precious outlet for sex, while Mirabelle, very mistakenly, sees Ray as a potential lifelong mate.
During a business trip, Ray has dinner with an old girlfriend. During dinner she propositions him and he accepts. Ray confesses the liaison to Mirabelle.
...
Ray apologizes for how deeply he hurt her and admits that he did love her.
Ray remarks that he had kept her "at arm's length" to avoid the pain of their inevitable breakup, but that he is hurt by the loss regardless.

'As Ray Porter watches Mirabelle walk away, he feels a loss. 'How was it possible?', he thinks. 'To miss a woman who me kept at a distance, so that when she was gone, he would not miss her. Only then does he realize how wanting part of her and not all of her had hurt them both.'