'I Had a Breakdown': David Harbour 'Ashamed' and 'Embarrassed' by His 'Erratic Behavior' After Lily Allen Split

David Harbour revealed the ongoing drama in his personal life led to a "breakdown."

Rumors popped up in late 2024 that the actor and Lily Allen separated, and the singer quickly channeled her heartbreak into music, going on to write a scathing breakup album that painted the Stranger Things star as a cheater.

Things got worse for Harbour during 2025, as multiple reports surfaced about him acting out both on and off the set.

"I had a breakdown. I do suffer from some confusing stuff — it’s confusing as h---," he told Variety in a new interview of his bipolar diagnosis. "I think a lot of people have a friend or a brother or a co-worker that deals with mental health stuff, and they’re probably pretty confused when that person gets depressed or gets manic or has an episode."

"Under times of extreme stress, that can cause somewhat erratic behavior, and it’s embarrassing, and I’m ashamed of it. It’s not something I choose, and I wouldn’t wish it on my worst enemy," he continued. "I do feel like, for some of us, our gifts are inextricably linked with our illnesses."

"To have a nervous system that reacts to the world in a too-delicate way can allow me to have that moment that I love on the swings with [DTF St. Louis costar Jason Bateman]. But it can also force me, in moments of extreme stress, to act a little weird," the star, 51, pointed out.

Harbour refused to get into the nitty gritty of his breakup from Allen, 41, but called her salacious West End Girl album "weird."

"I do believe that it is the privilege of every artist to use their experience to create art, and so I respect her for doing that," he explained. "I can’t really say that much more, because it’s my private life. In spite of the fact that a lot of people don’t allow me a private life — I value it. And I also value the lives of the people that I interact with privately. I just won’t speak about that."

"Stories are complex, and that’s why I say I respect her creation of art to channel her experience. It wasn’t my experience," he concluded of her new music.

Allen hinted she and her ex had an agreement that they could sleep with other people under certain conditions, such as keeping it discreet and completely no strings attached. The singer made it seem that he didn't keep his promise.

Harbour also faced scrutiny relating to a harassment claim Millie Bobby Brown made against him, but the two have since resolved the issue.