After a painful divorce, Beverly Hills, 90210 actress Jennie Garth opens up exclusively in this week's issue of PEOPLE about losing 30 lbs., pulling her life together after her eleven-year marriage to Twilight's Peter Facinelli ended, and diving back into the dating pool. "I spent a couple of years lying in bed and being depressed," Garth tells PEOPLE. "Physically, I didn't look my best, and mentally I didn't feel my best. I was doing everything I could to be a good mom, but that was all I could handle."

After several months of introspection and isolation, not to mention her milestone 40th birthday in April, Garth realized she needed to get herself back in the game. "I just looked at it like there's no way I can hide out in the country and never work again, never love again, and never laugh again," says Garth, who moved from the Santa Ynez, California ranch where she had retreated after the split to Los Angeles in July with her and Facinelli's three daughters, Luca, 15, Lola, 9, and Fiona, 6.

The past year, she explains, "has been a bit of a rebirth for me as a person by shedding that negative space and all the pain associated with that time." Emotional baggage isn't all that Garth lost: The newly svelte actress has dropped "30 lbs. of dead weight." After all, she jokes, "sitting around on the couch eating Pringles all day is not going to help anybody." Thanks to twice-weekly sessions with a personal trainer and more sensible eating habits, Garth regained her girlish figure, which she now has on display in her new Old Navy TV commercial with former 90210 pals Luke Perry and Jason Priestley. Perry can't stop raving about his pal's amazing transformation. "She looks fabulous," says Perry, who is developing a sitcom with Garth. "She has the ass of a 25-year-old!"

That energetic reception is just what Garth needed after enduring the painful transition this year from married life to single mom. "I'm not pining, and I'm not sad," she says about her divorce from Facinelli, 38. Thanks to support from family and friends and "a lot of introspective work," she says she has come through the experience a stronger person. "I have a strong constitution," Garth says. "I have a lot of inner calm about stuff right now."

Of her daughters, "Peter and I are certainly putting them first. We're working really hard to be the best co-parents that we can be," she says. One thing Garth wants her kids to know is that while they are truly loved, life isn't perfect. "My mom did a great job of raising me, but she made me feel like I was a princess. I don't want to give my girls that misconception of life because life is tough and you're going to have struggles," she says. "But you are worthy of success and happiness and love."

That last lesson is one that the now-single Garth has taken to heart herself. Reentering the dating world "is weird and exciting," she tells PEOPLE. "Sometimes it feels awkward, and sometimes it feels really natural." For the first time in a long time, she admits, "I just want to love and be loved."

Jennie Garth reveals how she lost 30 lbs. in the 10/15/12 issue of PEOPLE, on newsstands everywhere now.

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