Since Justin Theroux dumped Heidi Bivens — his live-in girlfriend for 14 years — and took up with Jennifer Aniston, Bivens has taken solace in the company of menswear designer Rogan Gregory. Theroux’s costume-designer ex was seen with Gregory at the Persol Magnificent Obsession party in Chelsea Thursday night. We reported that Bivens moved out of the apartment she shared with Theroux a few weeks ago and is “heartbroken” about the breakup. Bivens and Gregory mingled with guests including Sir Ben Kingsley, Shenae Grimes, Famke Janssen, Rebecca Minkoff and Lance Bass.