The irony of marriage
The irony of marriage is demonstrated through the plot, because Oliver thinks marriage will be one way, but when he encounters the way life challenges couples, he realizes that his expectation was ironically insufficient. He believes marriage is something perfectly enjoyable and fulfilling, but actually his marriage to Jenny changes his perception. At the end, Oliver must realize the ultimate value of love, which is that love is a sacrifice.
The secret sickness
The sickness is ironically concealed. Oliver is afraid of hurting his wife and his family by telling them the truth about Jenny's prognosis: She's dying. The secrecy is ironic in many ways, but perhaps the most thematic irony is this: Life is willing to harm Jenny, but Oliver doesn't want to. The secrecy indicates Oliver's desire to make people feel better, but this time, there is no escaping the absolute horror and sadness that life has offered them.
The irony of death
Death is the ultimate irony in this film because it seems unexpected. That's exactly the point. By offering a boy-meets-girl story, the audience is suspecting a Love Story in the romantic sense, but instead, the idea of love grows to encompass the ultimate problem of human life, which is death. Oliver has to mourn his wife, which is the movies way of bringing romance to its ultimate conclusion.
The ironic union with father
In the end, the father and son are reunited under the banner of suffering and loss. This is ironic, given that the title of the movie makes the audience suspect that the movie will be about union between a wife and husband, but this movie is more about family love than romantic love, suggesting that as a person grows in maturity, they are much more likely to forgive, to preserve a family instead of rending one apart.
Love and sacrifice
These ironic qualities help to point the audience toward a seriously challenging irony, that love is not about fulfilling desires (although that is the lure that love offers; it is like a bait and switch). Oliver can't help but think that his marriage will fix his life and his problems, and his self-perception too. But instead, love slowly asks Oliver to sacrifice greatly. He has to sacrifice everything. By the end, he hasn't gained a wife; he has lost one. Love came to his life to take away, not necessarily to give.
