• The protagonist is a US politician running for election (of US senator I believe, or else possibly US president or US congressman).
• The politician has a love relationship and for some reason (I forgot why), he has to choose between dating the woman or running for office. The relationship is based on romance/love (it's not a sex-only relationship). From what I remember, the politician is a single person, so it's not an extra-marital affair and there is no unfaithfulness involved on his part.
• As far as I remember, it's neither comedy nor science fiction, but a serious film (romance/drama).
• release date: 1990-2015, not older I think
• My faint memories suggest that the woman disappears (at least for a while) and the politician is looking for her.
• I'm a bit lost as to who the actor was, but AFAIR the character was a young and upcoming politician, so I think the actor was looking rather young. Younger than Michael Douglas for example. I was thinking someone in the mold of Josh Hartnett, Ryan Gosling or Matt Damon maybe. But I looked through their cinematography and found no matching film. Could be a totally different actor of course. (My first guess was Josh Hartnett, but one of my favourite films is Wicker Park, in which Hartnett searches for a woman, who has disappeared, so I hope this plot doesn't erroneously bleed into point 4 above.)
Thanks for your help. Your film indeed fits the description, but unfortunately it's not the film I'm looking for. Any other films that come to your mind ?
Thanks Dardan. The Adjustment Bureau would be a perfect fit (Matt Damon, politician, election, woman, forced to separate, etc.) but it's science fiction, whereas I remember my film to be one supposed to take place in our real world. I added that to the clues in my OP to further narrow down the film.
"The Candidate" (1972) I know its a little bit older but some of the plot points you mentioned definitely fit so I figured it was at least worth mentioning. It is about a man running for the Senate and he does have an affair. It stars Robert Redford. "True Colors" (1991) It is about a man running for a Congressional seat. I don't remember an affair but the man running for congress commits a lot of acts of corruption. It stars James Spader and John Cusack. "Bob Roberts" (1992) It is about a man running for the Senate. I don't remember an affair. It is shot documentary style. It stars Tim Robbins. "Dave" (1993) It is about a man who looks like the current President who is used to cover up the President's extramarital affair. It stars Kevin Kline. "Primary Colors" (1998) It is a *fictional* telling of Bill Clinton running for the Presidential election in 1992. It involves allegations of an affair that is covered up. It stars John Travolta. "Bulworth" (1998) It is about a man running for re-election to the Senate but is depressed and suicidal about the state of politics that he hires a hitman to kill him and then lives it up for his final few days of life. It stars Warren Beatty.
) 
