Unfaithful

I got this moive quite sometimes, but have not watched it as yet. What a silly me! I bought it with Region 1 or something... but my player doesn't have access to that Region. Maybe it is too old? Anyway, even though I've not watched it I seem to know the plot of it.

It is just coincident that I feel the word "unfaithful' is attacking me. Am I unfaithful to you? Or Are you unfaithful to me? When we are committed, is it right to hold someone else in our arms? and come back to your lover that .. "now I know how much that person meant to me"

Who is unfaithful, tell me?