The 27-year-old actor decided to break up with Stewart after she ignored his pleas to take their relationship slowly, reported Contactmusic.
"Kristen wanted to go straight back to where they'd been before they first split up and pushed Rob really hard on it. She wanted the whole package: the house, the wedding and even the baby. It was all way too much for Rob to handle.
"If Rob had got his way they would still be dating but taking things slow," a source said.
"Rob asked for space and it sent her over the edge. She told him if he wanted a break, it would be permanent."
Stewart is reportedly furious with Pattinson because she feels like he took the easy way out.
"Rob has been a mess. He's the one that ultimately pulled the plug, but that doesn't mean it's any easier on him. Rob loves Kristen and he truly wanted to spend the rest of his life with her," the source added.