The Ghost actress, 49, is said to be heartbroken after photographs came out showing Rihanna leaving Kutcher’s home at 4am.
A source said: “Demi is constantly keeping tabs on Ashton so when these pictures came up she was understandably devastated. Demi’s convinced something happened between them and said she felt ‘sick to her stomach’.
”Demi’s been acting crazy ever since, trying to find out information about the pair. Demi is in such a fragile state, even the idea of them together has affected her quite badly.
”She’s in a terrible way but, at the end of the day, Ashton is a single man and free to do whatever he likes.”
Kutcher, 34, and Rihanna, 24, are rumoured to have been having a secret fling over the last eight weeks, after meeting at a mutual friend’s house party in December.
Moore was recently admitted to rehab, following the pair’s split in November, allegedly for an eating disorder and addiction.
Another source said Moore felt “humiliated” because Kutcher seems to have moved on so quickly after her stint in rehab.
The insider said: “She’s really hurt by the rumours and feels humiliated he’s being linked to other celebrities just a few weeks after she got out of rehab.
“She feels it cheapens their marriage even further.”