Country Strong

The film begins with Beau (Hedlund), singing with Kelly (Paltrow), a recovering alcoholic going through rehab. Beau is clearly smitten by her, and it is later revealed that the two have been having an affair, even though Kelly is married to James (McGraw). Kelly is checked out of rehab a month early by James, who wants her to go on a three-city tour to restore her image. She agrees on the condition that Beau becomes her opening act, but James has already made plans to see Chiles Stanton (Meester), a beauty queen with potential to become a rising singer, perform that night in hopes that she will be Kelly's opener instead.
On the night of Chiles' performance, it is revealed that Beau has been acquainted with her before and doesn't want her on the tour, dismissing her as a "Country Barbie". Chiles' performance nearly falls apart as she gets stage fright and can't sing; however, Beau steps in and begins to sing "Friends in Low Places". The two sing the song together, and it gives Chiles the courage to continue on her own. James is impressed by Beau's performance, and offers the opening act to both Beau and Chiles. He suggests to Beau that he and Chiles could make quite the duo, but Beau disagrees. Nevertheless, Beau agrees to go on the tour because he cares so much about Kelly.
The first show is a disaster: before going on, Kelly receives an anonymous package containing a bloody baby doll with a note reading "Baby Killer," referring to the baby Kelly miscarried when she fell off the stage in Dallas during her last concert before she went into rehab. At that concert, she was five months pregnant and was found to have a blood alcohol level of 0.19 when she was in the hospital for the injuries related to the fall. Kelly falls apart, starts drinking, and almost refuses to go on. However, she is coerced into going on stage by James. She begins to sing "Country Strong" but breaks down on stage. She attempts to try another song, "A Fighter", but breaks down again and is led off stage by her husband, ending the show. They tell the media at a press conference that they had to cancel the show due to food poisoning and head off to the next show.
Beau ends his relationship with Kelly, and begins to spend more time with Chiles, whose fame has been increasing as the tour progresses. Both Chiles and Beau form a bond and Beau lets go of his earlier hostilities towards her. She even finishes the chorus to his song "Give in to Me".
Later, Beau confronts James about Kelly's worsening condition. James insists that Kelly may get better, and says that he can't let her go out with a failure. Beau disagrees and subtly admits their affair. Enraged, James punches him in the jaw and leaves the room.
Before the next show in Austin, Kelly gets drunk and is unable to go on stage. Beau and Chiles still do their opening act, and it is then that they perform "Give in to Me" for the first time together. JJ, Kelly's agent, nearly cancels the tour but is dissuaded by Kelly's offer of sex. Beau witnesses this and becomes frustrated with Kelly. That same night, Chiles and Beau have sex, and Beau confesses to Chiles that he likes her.
In Dallas, Beau gives Chiles a pair of star-shaped earrings she had said she always wanted and asks her to move with him to California. Chiles immediately says yes, but changes her mind and asks him for time to consider the offer.
The two perform and Kelly comes out, this time sober and ready, and performs her entire set for the first time. Kelly is seen performing "Country Strong", "Shake That Thing", and "Coming Home". After the concert, James and JJ immediately begin making plans for Kelly's future. That night, Kelly commits suicide by overdosing on prescription medication. She leaves a letter to Beau, echoing his earlier words that "Love and fame can't live in the same place." In the letter, she gives him the advice to choose "love". Beau takes her advice, and after Kelly's funeral, he moves to California.
Later on, Beau is seen singing in a bar in California, and he sees Chiles walk in, wearing the earrings he gave her. The film ends with the two singing the song they wrote together, "Give in to Me".

Question: Who does Kelly have an affair with?
Answer: Beau