The pair are rumoured to have consummated their relationship when Bannerman visited the singer's home in Wales earlier this week.
They met for the first time since the jungle while posing for pictures at the Sloop Inn in Porthgain, Pembrokeshire, where Matthews and ex-husband Seth Riddle held their wedding reception four years ago.
A source told the Daily Star that they then spent three days at Matthews' house in Fishguard, saying: "They locked the doors and steamed up the windows."
The ex-Catatonia star is thought to have introduced Bannerman to her children Glenys, four, and Johnny, two, leading friends to believe that the relationship is progressing quickly.
The source added: "That's a clear sign she believes they have a future together. Marc and Cerys have been texting, emailing and chatting on their mobiles ever since the jungle.
"But they couldn't wait to be back together again. She never dreamed she would find love when she set off on her I'm A Celebrity... adventure. But that's exactly what's happened."