With millions at stake, it must have been one hell of a bust-up that split the Spice Girls. But that's female friendships for you, says Lucy O'Brien

LAST SUNDAY Geri Halliwell's shock announcement that she was leaving the Spice Girls ended days of speculation. "This is because of differences between us," she said. With a move that will contractually cost her millions, we can assume this is the understatement of the year. The bust-up, apparently centred around a power struggle between Geri and Scary Spice Mel B, must have been spectacular.

One of the fundamentals of Girl Power, female friendship, has cracked. Geri's friendship with the rest of the Spice Girls was passionate and intense, but now they have fallen out, it appears irretrievable. And it's not just high profile girl friendships like Geri and Mel B or Sandra Bernhardt and Madonna that founder under the weight of their own expectations. Women's friendships often have the intensity of romantic attachment, so if they fall out, it is with all the tears and trauma of jilted lovers.

"When I first met Gina she was extremely good-tempered, joyous, intelligent. We met at a work function and ended up going home, chatting the night away. We were close from then on, but after a while she became very insecure and competitive, and she would bad-mouth me behind my back," recalls Theresa, a 28-year-old health worker. "In the end I phoned her to say we had to part company. She insisted we meet for a last goodbye, and she tried everything, she wept, she clung to me, promised she'd love me forever. That was a year ago, and we haven't spoken since."

Theresa's friendship had all the passion of an affair, even thougn it didn't become sexual. While some gal pals end up sleeping together, even those that don't have an incredible emotional intimacy with their best friend. "Mothers teach their daughters to be like them," suggests psychotherapist Susie Orbach, co-author with Luise Eichenbaum of Between Women: Love, envy and competition in women's friendships. "But at some point, because of having to be heterosexual, girls feel unconsciously pushed out by the mother, and there is part of them longing to connect up again with feminine sensibility. In female friendship a woman feels she has been understood at a very deep level. So if they fall out, it can be devastating."

Girls learn early on to mirror each other's experience, sharing their deepest secrets in a way that leaves them vulnerable. When Jill broke up with her best friend at school, she felt so betrayed, she sought only the company of men for the next four years. "It's much cosier when you're friends with blokes. You can have matey-matey friendships that wax and wane without feeling too traumatised," Jill says. "But after a while I missed having a best friend I could get drunk with and talk to in the small hours. It wasn't until I went to college that I stopped being wary."

People change, and while in sexual relationships partners confront changes with conflict or conciliation, ordinary friendship rarely have recourse to anything so formal. Linda, 32, found it a strain when she shared a flat with her best friend since childhood. "Susan was in control, sensible, organised. I was prettier but more chaotic. A mess. The older I got, the more I sorted out, and the more I realised I didn't want to be that person any more." The change caused painful friction, with a mound of unspoken irritation building up. "The thing is, you're not allowed to row with a best friend. It has all the intimacy of marriage without being able to let off steam." The pair sold up "on chilly terms", and have seen each other intermittently since. "I was very sad about it," says Linda. "We may rescue the friendship, but it'll never be the same."

The challenge for women, it seems, is to openly acknowledge feelings of envy and difference. A friend recently told me how her closest girlfriend had been severely niggling at her on the way home from a holiday. "In the past I would have kept quiet, but that withholding is a form of hostility. So I told her to fuck off. In the end we talked about it and were able to laugh."