Happy Accidents (2000)

Ruby Weaver (Marisa Tomei) is weary of her long history of failed relationships with men when she meets Sam Deed (Vincent D'Onofrio) in a park. But after the two fall in love, Ruby becomes suspicious of Sam's past and under pressure from her, he finally explains that he is really from the year 2470 and is what he calls a "back traveler". Ruby initially ignores this story, considering it yet another case of male nerdy weirdness, but after Sam's persistence, apparent conviction, and growing agitation, she begins to wonder.
Finally she takes him to see her therapist (Holland Taylor). Ruby becomes worried as to Sam's sanity when he states that everything he has done was a deliberate attempt to change her life. At the close of the film it is revealed that not only Deed, but the psychologist too, are in fact "back travelers," and Deed is shown using the emotional component of a controversial idea called the Cheeseman Theory to reverse time himself in order to save Weaver from being hit by an onrushing car that had killed her in her previous lives.