The Coronation Street actress, 37, started dating her personal trainer just two months after her divorce from actor Jamie Lomas was finalised.
"It was just too much, too soon for her," an insider told The Sun. "She has feelings for Matt but she was worried about rushing into a relationship."
"Kym explained how she felt," the source added. "Matt was disappointed but he understands the timing just isn't right for her. For the moment, she wants to concentrate on work and her family."
Kym and ex-husband Jamie, who announced that they were going their separate ways last October, are parents to two-year-old daughter Polly. Their son Archie tragically died moments after being born in 2009.
The actress is also mother to teenagers David, 18, and Emilie, 15, from a previous relationship with Dave Cunliffe.
Jamie moves on with new girlfriend Chloe Peers
The small-screen star spent last weekend's Mother's Day with her family, and posted sweet photos of her close-knit clan.
"Why can @EmilieCunliffe never just have a normal photo?? Haha nice face babe! Fam night in last night!" she posted alongside a photo of her and her daughter posing.
"Happy Mother's Day to the best mum ever!!! If I'm half the mum you are I will be ecstatic, luv you mum @marshyswife," she followed up the next day with another snap.
Earlier this month, Kym — who plays Michelle Connor in the popular ITV soap — was seen smooching up to 24-year-old Matt. The pair were spotted enjoying a walk in a park near the actress' Manchester home.
Kym's friends had previously said that while the couple had been taking things slow, Matt's romantic gestures had got Kym "smiling again". The gym fanatic had trained the actress for several years and so Kym's children were used to having him around.