As you think about your marriage, it's important to tune into both sets of reasons. Sometimes marriages erode over time, in ways that are so subtle that neither partner even notices the change. In other cases, there's a clear turning point in the marriage, after which the course of the relationship changes for the worse. In still other relationships, the behaviors of one spouse are corrosive to the marriage and sometimes to the other spouse. In fact, it's unfortunate that more people don't leave marriages where there's gross abuse and neglect that is neither good for them nor their children.
People choose to remain in such marriages for all sorts of reasons.
In other cases, people feel they have nowhere else to go, or no-one else will love them. Sometimes people stay because they simply don't realize they can leave. And it's not at all uncommon for people to stay in an abusive relationship because they fear leaving. Here, the best recourse is to seek professional, and possibly legal, advice and protection. Perhaps your marriage no longer meets your needs.