Melanie Griffith and Antonio Banderas ''have had issues for years.''

The 56-year-old actress filed for divorce from her husband after 18 years of marriage last week, citing irreconcilable differences and seeking spousal support and physical custody of their 17-year-old daughter, Stella, but their friends are shocked by the split, as the couple have always worked through their problems in the past.

A source said: ''They've been down this road before and had their ups and downs, but I never thought it would actually happen.''

But another insider said: ''They have had issues for years. The fights and separations got to be too much. There were fewer happy moments.''

The 'Shrek' actor, who supported Melanie when she underwent treatment in rehab for substance abuse in 2000 and 2009, was allegedly spotted getting cosy with two different women last year.

But a source close to the actor told PEOPLE magazine: ''I never saw him do anything that would be alarming. He has always been in love with one woman - and that was Melanie. They always had a very passionate relationship but also a very mature and secure one.

''She trusted him. If they were apart, he would call her all the time.

''He once said that things were better when they travelled away from each other. Because when they'd get back together, it was like a honeymoon all over again.''

Despite going their separate ways, the duo are still on good terms and optimistic about the future.

A friend close to Melanie said: ''Simply put, I think life took a toll on them. But they will be the first to say they had a good run.''