The Boyzone singer cheated on the model with a dancer in 2010. The couple officially announced their split in April this year after 14 years of marriage.
Yvonne is now dating cameraman John Conroy, who she met in February on the set of upcoming movie Dark Touch, which stars her daughter Missy.
"The news that Yvonne has found love again has hit him really hard. He was desperate to try to make her give him another chance, but by cheating on her like he did, Ronan broke the trust that once existed between them," a friend of Ronan's told the Sunday Mirror.
"He has made no secret of how much he is still hurting over the break-up of his marriage. Now he is having to try to accept that his wife is dating again."
Conroy, who has worked on films including Sweeney Todd, The Bourne Ultimatum and The Da Vinci Code, apparently left his wife Suzanne in January.
Ronan recently admitted that he is still struggling to come to terms with the split, saying he sees himself as a "failure".