We find out!
1 in 4 Brits has slept with a married person, according to UK Medix- so it would seem that neither the single or the married partners in crime are put off by having a wedding ring or a husband or wife in the picture.
Sarah Bailey of UKMedix.com commented on the findings:
“These results are certainly scandalous and not at all what we expected to find. The worst thing, I think, is that so many people who are up to no good just don’t seem to care about the damage they are doing. Even if a marriage is on the rocks or seems beyond repair, vows are made to be faithful through thick and thin. The fact that so many single Brits care nothing for that and would soldier on regardless with a married individual is really sad.”
With this in mind, we take a look at those celebrities who have had affairs with other celebrities or in some cases non celebrities and what repercussions it had on their relationships. 
Whoopi Goldberg
She publicly admitted that she had numerous affairs and in an episode of The View in April 2010 she defended Jesse James, then-husband of Sandra Bullock, commenting, "It's nobody's fault. Maybe he was looking for something different", adding that she had strayed from her marital bed.
Leann Rimes
Rimes fell in love with her back up dancer Dean Sheremet. They met when he danced for her at the 2001 Academy of Country Music Awards. She said after her first date with him that “This is the guy I want to marry", she told In Style Magazine.
The couple got married in 2002 but separated in 2009 and got divorced. There was lots of press coverage of an extramarital affair that had gone on between Rimes and Eddie Cibrian, whom she worked with on Northern Lights.
As a result, Brandi Glanville, Cibrian’s wife, filed for divorce and after eight years, their marriage was over. In 2010, Rimes publicly apologised for her actions; "I take responsibility for everything I've done. I hate that people got hurt, but I don't regret the outcome."
In 2010, Rimes and Cibrian got engaged and since that, her music career has been affected by her affair, with constant media coverage about the ongoing battle with his ex-wife.
Meg Ryan
Ryan married actor Dennis Quaid in 1991, after they were in 3 films together- she said she would only marry him if he stopped using cocaine and he did- so they tied the knot. While she was filinmg Proof of Life, she become involved with actor Russell Crowe and her and Quaid separated and got divorced soon after. In 2008, Quaid revealed that Ryan had been unfaithful to him for a long time while they were married.
Kristen Stewart
In 2008, Stewart began her relationship with her Twilight co-star Robert Pattinson but did not publicly confirm it until 2012. Photos of her and Snow White and the Huntsman director Rupert Sanders were leaked, sparking rumours of an alleged affair between the two. The same day Stewart released a statement apologising to Pattinson. "I'm deeply sorry for the hurt and embarrassment I've caused to those close to me and everyone this has affected. This momentary indiscretion has jeopardized the most important thing in my life, the person I love and respect the most, Rob. I love him, I love him, I'm so sorry."
Jesse James
James married Sandra Bullock in 2005 after they first met when she arranged for him to meet her godson at Christmastime. They both won legal rights to his daughter who he had with his second wife. In 2010 there were rumours that he was having an affair and she cancelled all her European promotion for The Blind Side.
In 2010, James responded to the rumours of infidelity by making a public apology to Bullock. He stated, "The vast majority of the allegations reported are untrue and unfounded" and "Beyond that, I will not dignify these private matters with any further public comment.” He followed this with; “There is only one person to blame for this whole situation, and that is me", and asked that Bullock and his children one day "find it in their hearts to forgive me" for the "pain and embarrassment" he caused them. He then checked into rehab and they later go divorced.
Angelina Jolie
Both Jolie and Pitt still claim to this day that there was no physical affair during the time they were filming Mr and Mrs Smith, however there may have been one of the heart. Each of them has come forward since and said that they fell in love with each other while the movie was being made. Make of it what you will.
Jude Law
Law met Sienna Miller while they were filming Alfie in 2003 and got engaged on Christmas Day in 2004. In 2005, Law made a public apology to Miller for sleeping with the nanny of his children. They split not long after but gave things another go in 2009, after they met while both performing in separate Broadway shows, before calling it a day again in 2011.
Source-Wikipedia.
tagged in Angelina Jolie Jude Law Kristen Stewart Whoopi Goldberg Robert Pattinson Sandra Bullock Affair