For months, confirmed an insider, Justin, 40, had been "calling, texting and e-mailing Heidi without Jen's knowledge. Another pal added that Jen had no idea until she caught Justin texting Heidi from the Hollywood home that they had just started to share: "In Jennifer's book, what Justin did was cheating
. He was going behind her back to maintain ties with his ex. She was furious and read him the riot act!"