Reid is alleged to have sent private Twitter messages to Amy Willerton, the 19-year-old who won ex-wife Katie Price's modelling competition Signed By Katie Price.
"She's extremely upset. She's in tears. This is a horrible situation for her. She wants to know what the hell is going on," a source told The People.
"This seems to have really left Chantelle very upset indeed. The pair of them now need to sit down and try and work things out."
The couple, who met last May, got engaged on live television last October and recently announced that they are expecting a baby girl.
"Alex has thousands of followers on Twitter and is asked to follow lots of people. Any private message to Amy was entirely innocent," his spokesperson insisted.
Reid split from Price in January 2011. He has had to delay his wedding to Houghton as his divorce from Price is yet to be finalised.
Willerton recently claimed that winning Signed By Katie Price had changed her life for the worse.