Loveless marriages are common. The biggest reason people not in love stay married is economic. Usually the wife either doesn't have a marketable skill or is too lazy to go out into the world to earn her own money so she stays in a dead marriage with a dudly husband and often the husband knows he has this power over his wife so he keeps her to raise his kids and keep up social appearances while basically doing what he wants on the side.
Studies done on social class in marriage found that if one is heavily dependent on the other for economic support, that person is less likely to cheat or initiate a break-up but if neither needs the other to get by, they're more likely to cheat and break up.
This probably explains why divorce rates have gotten so high in modern society. Women don't need men anymore to support them so they're more likely to bail than hang on to defective men.
The common pattern for divorce or break-up is that the writing is on the wall. Divorces are developmental.