Megan Fox Says New Movie 'Till Death' Shows That It's Better to Break Up Before You Cheat (Exclusive)

ET spoke with Fox ahead of the release of her new movie, 'Till Death,' which arrives in theaters and on demand on July 2.

Megan Fox's new movie definitely taught her some things about relationships.

While the 35-year-old actress' relationship with Machine Gun Kelley is going strong, in her new movie, Till Death, she's trapped in a nightmare of a marriage. While chatting with ET's Matt Cohen, Fox shared what her boyfriend thought of her edgy role, why it's unlike anything she's done before, and the lesson she learned from filming the horror-thriller.

"I don't know if it's very philosophical but a lesson from this movie, break up or get divorced before you cheat," she shares, adding that it "doesn't ever work out well for anyone. [Or you] could end up chained to a dead person."

Till Death follows Fox as Emma, a woman who wakes up handcuffed to her dead husband after a romantic evening at their secluded lake house. As she's trapped and isolated in the dead of winter, she has to fight off hired killers to escape her late husband's twisted plan.

Fox shared that her musician boyfriend has seen part of the edgy thriller, adding that he loves seeing her be a versatile actress. The two started dating last summer, after co-starring in Midnight in the Switchgrass.

"He's an actor as well as an artist, so he likes to see the different facets of what I can do for work or how I can push myself or be someone that I’m actually not," Fox says. "And how good I can hopefully be at accomplishing that and selling that."

"It was just different than anything else I had read or seen," she notes of her role. "I haven't done, like, a marriage drama before. I haven't done, like, a grownup movie. I haven't done a traditional thriller or horror movie before. Because Jennifer's Body was not that. It was very much, like, a teen, angsty, dark comedy. And this is not."

This week, Fox posted stills from the movie, captioning the shots, "Lessons on how to escape a toxic relationship." Her advice for not being in a toxic relationship, she says is "you just have to be aligned with yourself and you have to remove your ego as much as possible, which is of course a lifelong journey."

"I think you have to be selfless, meaning you have to always prioritize loving the other person where they are, as they are, who they are in this moment. Not try to change people and not project your own insecurities on some other people," she continues, adding that to make a relationship work, "You have to be a good listener."

The role, meanwhile, had Fox tied to a stuntman, dragging herself to safety. "He was amazing," she said of her co-star. "He was heavy, and I was chained to him the whole time. His job was to play dead, so he was like actually [acting] dead and I was handcuffed to him and I had to pull him around through all of the scenes. And it wasn't easy! I mean, I'm strong but not that strong. After hour 13, it kind of gets a little trying."

Fox, however, had "a lot of fun," sharing that she prefers stunt-heavy and really physical parts. "I have the best time making those," she relays. "I don't do well sitting still, talking all day, every day in a room. That's not as inspiring to me as something like this. So I had a great time. I'll always choose movies like this over something that's more contained."

Till Death arrives in theaters and on demand on July 2.