I heard a new phrase today and it generated all sorts of mental images. The phrase was crossing the Rubicon, the idea is that you deliberately go past the point of no return. The origination of the phrase is to Julius Caesar's day, where he sent his army across the Rubicon River, starting his invasion of Ancient Rome. Once his people crossed that river, there was no turning back, the war had begun.
I heard the phrase in a commercial for an anti-divorce book or program to be used by couples. The individual said that he and his wife discussed divorced and nearly "crossed the Rubicon".
I know two couples whose marriages are in trouble and this image fits very well. One couple has already crossed the Rubicon, the second is close, if not already past. The image is that they are headed to this point, in some cases with increasing speed and the force behind them continues to push them. At some point, and you could almost draw a line, they have no way out.
An oft used equal phrase is burning bridges and a less used phrase is burning boats. I think it was Cortez who ordered his boats burned when invading Mexico to keep his troops from attempting to retreat.