"People weren't rooting for a good relationship," Kennedy tells PEOPLE. "That was really hard to deal with. You see snarky headlines and eventually you just have to stop reading that stuff."
Kennedy, 42, dated his Ghost Whisperer costar, 33, for a year before the relationship "ran its course".
"I guess it just comes with the territory," Kennedy says of dating in Hollywood. "She sneezes and people write about it."
But Kennedy looks back at his time with Hewitt fondly and credits her for giving him the insight to continue to persevere as an actor, writer, comedian and producer.
"When we were dating she told me, 'I'm celebrating my 20th year [in the business],' " Kennedy recalls. "She said, 'You have just got to keep moving. Don't stop.' "
And he is not stopping. Kennedy recently debuted as the host of the new The CW game show Oh Sit! (Wednesdays at 8 p.m. ET), which he calls "so weird, different and crazy."
"I've been part of some cool touchtone moments in pop culture," said Kennedy, who has also starred in the Scream series and Baz Luhrmann's Romeo + Juliet. "It's just about keeping that going and experimenting."
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