The Irony of Coincidence

We first meet our protagonist, Jessica, when she discovers she's pregnant. In a flashback, we her meeting her baby daddy while dancing at a club in L.A. with her childhood friend, Jenny and her partner Taylor. Flashing forward, on a date with this same older man, Mark, a doctor from New York, we find out he is married or (separated but not yet divorced, according to him). Upon finding out, Jessica doesn't disclose her pregnancy, only that she is moving to New York after getting a new job.
We then meet Mark's wife, Sarah, an OB/GYN on a trip to L.A. for a medical conference when she gets a call from her sister, Tiffany that their mom had her second heart attack and must book the next to flight to New York.
Jessica and Sarah incidentally get on the same flight to New York and coincidentally end up seated next to each other on the plane. They connect from the beginning when Sarah asks for the aisle seat. Sometime into flight, Jessica realizes through her social media that Sarah is Mark's wife! Meanwhile, Mark has joined Tiffany at the hospital where Sarah's mom has gone into surgery. More than halfway into the flight, there is a weather emergency. The plane makes an emergency landing close to D.C.
Finding herself in a rush to get to her mom and with no flights left for New York until early morning, Sarah is forced to ask Jessica who has rented a car for a drive to New York together, given the car rental place is out of more cars to rent. Out of guilt, Jessica feels pressured to agree given the gravity of the situation. While in the car, Sarah gets on a call with Mark to let him know what happened.
They get on the road, and their chemistry is still the same as on the plane, conversing very naturally, except now Jessica knows who Sarah is, but Sarah doesn't know who Jessica is.
Mark is blowing up Jessica's phone so much that she asks to make a stop at a gas station to use the bathroom and get snacks. She calls Mark while she is at the gas station to ask to stop texting and calling since she is with his wife! Mark is flabbergasted at receiving this information but good at playing it cool with Tiffany who is incredibly anxious waiting on her mom's surgery.
Jessica and Sarah get into an accident after Jessica is blinded by the headlights of an oncoming car. The crash is bad enough for another driver to call an ambulance. During this time, Sarah learns Jessica is pregnant.
Yet another holdup is when they get a flat tire after leaving that hospital due to the back window breaking during the accident. Being only thirty minutes from the hospital where Sarah's mom is and out of options, she calls Mark to come pick them up.
They finally get to the hospital. Sarah asks Mark to get Jessica in a cab. Meanwhile, Tiffany, Sarah's sister heads outside and notices Mark talking to Jessica at a point where they are being loud. Jessica heads off without noticing Tiffany walk up to them. However, Mark has to provide an explanation to Tiffany for what she saw and makes up an excuse that she works at the hospital.
Sarah's mom doesn't make it. The funeral takes place, and then at the wake, Mark is forced to come clean after Jessica shows up, and Sarah figures it all out proceeded by Tiffany making a scene in front of all their relatives once she realizes he'd been cheating.
Jessica settles into her new apartment and starts her job, where her coworker, Tom becomes her first friend. She tries to contact Sarah unsuccessfully until she has a miscarriage shortly after one night. Sarah answers and being an OB/GYN, takes Jessica to her clinic to check her up. Jessica apologizes profusely, but they don't reconcile. Jessica decides to give it one last try through a letter she writes.
Mark shows up at Jessica's work to try to work things out, but at this point, she is through with Mark as he tries to excuse his behavior instead of taking responsibility. The relationship is not salvaged. Mark does the same with Sarah with the same disappointing result to him. Jessica decides to give it one last with Jessica and writer her a letter.
Tiffany encourages Sarah to process what she's been through. While visiting, Jessica's mom, Laura does the same. After Sarah's last divorce proceeding with Mark, she finally contacts Jessica in response to her letter. They are finally able to reconcile at this meeting at Central Park.
Five years later, Jessica is about to publish a book that seems like a story about her and Sarah. She is pregnant with Tom as her partner. She still has nightmares about her car accident while pregnant the first time, but Tom is a great partner and comforts her. Sarah and Tiffany, as well as old friends, Jenny and Taylor who are about to get married, all show up to her baby shower. She learns from Tiffany that Mark is getting married to 23-year-old nurse.