“It’s sometimes a hard pill for a man to swallow when he’s with someone that’s, you know, successful,” says Kacey Musgraves, resting a manicured finger on her temple and gazing at her dressing room wall from behind lavish false eyelashes. “Someone that’s doing their thing, knows who they are, is comfortable with their sexuality… whatever. It can be intimidating for some men out there.”For a long time, the 30-year-old Nashville country singer found herself in this type of relationship. “Being with the wrong people can really do a number on your self-confidence,” she says. “I started to not really think that much of myself.”We’re backstage at Wembley Arena, an hour before Musgraves is due to play her biggest UK headline show to date. Dressed in a fluffy, baby-pink jacket and leopard-adorned leggings, she’s both a little frazzled over a last-minute costume malfunction – I’m told a tailor might have to come in and work on her while we chat – and nervous about the “big concrete cave” in which she’s about to perform.“You can’t really see anyone’s face,” she says, “so the audience is very anonymous unless they’re jumping out of the seats… which I know that Brits don’t do.” They do sometimes, I protest. “They can, but… I feel like, most likely, they’re gonna be kind of reserved.” I’m not sure if she’s underestimating British enthusiasm or her own popularity, but in a few hours the entire arena will get to its feet and sing along, a cappella and word perfect, to one of Musgraves’s early singles, “Merry Go Round”. We’re a long way from Nashville, but her sound has travelled far.Hers is a unique kind of country music. Until recently, primarily because of those confidence-shattering relationships, Musgraves mostly steered clear of one of the most dominant themes of the genre – love. Instead, with her warm Southern twang and a wit that flits between silly and scathing, she covered topics most of her peers wouldn’t touch with a barge pole – casual sex, marijuana, macho culture, slut-shaming, the stronghold of religion, and queer acceptance among them.“Make lots of noise, kiss lots of boys, or kiss lots of girls if that’s something you’re into,” she sings over slide guitars and affirming shouts on 2013 breakout single “Follow Your Arrow”. “When the straight and narrow gets a little too straight, roll up a joint… or don’t / Just follow your arrow wherever it points.”