El Moussa is parent to two children with ex-husband and "Flip or Flop" co-star Tarek El Moussa, from whom she split in December 2016 after seven years of marriage.
She started dating Anstead in November.
"Ant has been so supportive. He's very grounded," the HGTV star said.
"As he entered my world, there's so many false stories spinning out there and he's never said one word to me about any of it."
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"He always just says, 'You're an amazing person. You're amazing mom. You're an amazing girlfriend.' He's so positive with me that he's just really lifted me up in so many ways," she added.
El Moussa called herself "the luckiest girl" following an outing with Anstead and friends Wednesday in New York.
"Seriously love these 3 so much!!! @cazeb @shanrbeauty thank you for being so supportive and such strong #girlbosses you both inspire me daily, love you to the [moon]. @ant_anstead I'm the luckiest girl on the planet to call you mine. You complete me," she wrote.
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