Jennifer Lopez on Happiness, 'Marry Me' and Her 'Beautiful Love Story' with Ben Affleck

Jennifer Lopez has all sorts of reasons to be grateful — and very happy — these days.

For one, her film and music career is as hot as ever — her romantic comedy, Marry Me, is out Feb. 11. Her kids, 13-year-old twins Max and Emme, are happy and healthy. And over the last few years, she says she's dug deep to reach a place of inner peace she could only dream about for most of her life.

"I've never been better," the 52-year-old star tells PEOPLE in this week's cover story. "It's just that we're all in a very beautiful moment."

And yes, a certain tall, handsome guy named Ben Affleck has a little something to do with it.

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"I feel so lucky and happy and proud to be with him," she says, reflecting on their rekindled romance from the sun-drenched room in her house that's become Affleck's office when he's there.

"It's a beautiful love story that we got a second chance."

After the couple, who first dated from 2002 to 2004 but called off their engagement, reconnected last spring and sparks flew, they "had a little bit of fear," says Lopez, acknowledging the circus that surrounded them the first time around. "Before we kind of put [our relationship] out there and we were naïve and it got a little trampled."

This time, she says, "We both were like, 'Wow, we're so happy and we don't want any of that to come into play again.' We're older now, we're smarter, we have more experience, we're at different places in our lives, we have kids now, and we have to be very conscious of those things. We're so protective because it is such a beautiful time for all of us."

She adds, "I just feel very happy and lucky to be in a relationship that's happy and loving, and I want to do everything I can to protect that and keep it safe. It deserves that, it really does. ... We hold it sacred."

But nearly two decades later, things are different. "It's beautiful the way it feels very different than it was years ago. ... There's more of an appreciation and a celebration for it, which is nice," says Lopez, who treasures their second chance at love. "When you find somebody and you really, really love them and you get a second chance at that? That is a really rare, precious, beautiful thing and we don't take it for granted."

While she agrees it can be delicate bringing kids into any new relationship, she says, "I honestly believe that love rules all. Love always conquers everything — relationships, kids, work, work relationships. It's all about how loving, open and accepting you can be. Not having an ego about things and just embracing all the good, always looking at the positive."

"When you're in a good, healthy relationship, everybody benefits from that. Everybody."

A loving and respectful partner, Affleck, 49, has put in the hard emotional work to better himself along the way, she says. "I'm so proud of the him, I'm so proud of the man he's become that I've watched from afar. Being honest with each other, being loving, that's just the basis of everything," Lopez says. "I feel like he's at a place in his life where — just like how I feel about myself — it's been a journey of learning yourself and figuring yourself out, getting to a place where you feel really good on your own and who you are so you can be in a happy, healthy relationship."

She adds, "To see the person, the human being, the man that he is today, the father that he is today, the partner that he is — he is so everything I always knew he was and wanted to be."

Real-life fairy tales can be "a tricky thing," Lopez allows, but she's still a believer. "What I can teach my children is that real love exists," she says. "Some things can be forever, but it doesn't mean they just have a straight line."

As for what the future holds with Affleck, Lopez puts it this way: "I just want my future to be full of love and happiness, with my children and my partner. I think everybody just wants to be happy, with somebody to go on the journey with and grow old with, and I feel good about that right now."

In her new movie Marry Me, Lopez plays a pop star who marries a stranger (Owen Wilson) after her fiancé (Maluma) is caught cheating. The role was "really fun and also cathartic," says Lopez, who coproduced the film and enjoyed "revealing a little something of what it's like living in the public eye." Lopez also performs the soundtrack, which features original songs by her and Maluma. "The songs tell the story just as much," she says.

For the full, exclusive interview with Jennifer Lopez — and more extraordinary love stories — pick up a copy of PEOPLE's new Love Issue, on newsstands Friday.