The folks at Babble.com have put together a divorce checklist. They admit that everyone is different, and this isn't a one-size-fits-all list, but it's a start. Here are the signs:

Scratch That Whole “Best Friend” Thing (If you consider six other people your BF before your spouse -- that's trouble)

There are Outbursts (Out of the blue, your spouse blurts out "I feel we've had no connection for years." Ignore at your peril)

You Are No Longer... Romantic ("being physically indifferent to (or repulsed by) your bedmate is no small thing")

You Fantasize About An Affair

There Is Dread (Not looking forward to them coming home from work)

You're Drinking Too Much

You Are Watched (hiding your journal, email and cell phone is no fun)

...Or Watching

There Is Frequent Rolling of the Eyes

One Of You Is Happy (If one is unhappy, both are unhappy)