Women also leave and get a divorce because of physical, mental, and emotional abuse by their spouse. Women also leave and get divorced because the kids are being abused by the husband and it is the only way to save them. Women also get divorced because they believe they don't have to sit at home and wait for her husband night after night to come home and crawl in bed next to her while smelling of sex and another womans' perfume. Women leave because they have as much right to leave as men.
All that's been said by multiple posters already.
The "I love you but I'm not in love with you" is a huge red flag dude. Assuming you have been a good husband, are not a drunk, a serial cheater, or beat her, the alternative is she has already found someone else, and is in "the fog".
In the absence of that women rarely leave because they're bored or "have fallen out of love". They might start an affair because they're bored and that might lead to them leaving, but the affair is usually the tripwire. If the husband's been a douche then that's a different story, but barring that type of behavior the vast majority of the time they trot out the "I love you but I'm not in love with you" line it means they're sleeping with another guy.
