When Styles introduced "Boyfriends" at Coachella for the first time, he quite literally said, "To boyfriends everywhere, f*ck you." It's a song that's truly about boyfriends, specifically those who don't act right, with lyrics like, "Boyfriends, they think you're so easy / They take you for granted."
When talking to Apple Music, Styles said of the song, "I think the good part of it is that it is everything. It's both acknowledging my own behaviour. It's looking at behaviour that I've witnessed. I grew up with a sister, so it's watching her date people and watching friends date people, and people don't treat each other very nicely sometimes ... And it was kind of one of those, it was one of those really quick, just say what you think of boyfriends."
Interestingly, the song also starts with the last line of the song reversed. The song ends with, "Feel a fool, you're back at it again," which sounds like gibberish in reverse at the beginning. However, this feels like a symbolic way of showing the cycle of getting caught up in your feelings and continuing to go back to that person you can't escape.