Codependence can be defined in a variety of ways. Often, it is used to describe a romantic relationship where one partner enables another partner's substance use disorder. Other's might say it is when two people with low self-esteem stay in a relationship to avoid loneliness and keep their self-esteem on life support, in spite of many intractable problems or irreconcilable differences.

Through my work with clients, I have developed what I believe to be a more universal definition of codependence. Here it is:

Codependence is
allowing your own happiness
to depend on another person
acting in opposition to their usual behavior.

Regardless of the reason, if you need a partner that does a particular thing in order to be content in a relationship, and your partner has a difficult time doing that thing consistently—or has never done that thing, or does the opposite of that thing—this indicates a need for very serious examination of this aspect of the relationship.

This definition of codependence doesn't involve judgment of either partner.
Instead, it shines light on a profound mismatch in relational needs and capacities.

For example, it's important to Alex that their partner, Bailey, is close to Alex's family, and Bailey may rarely join Alex for family visits. This may be because of social anxiety, differences in family-of-origin experiences, or Bailey's negative experiences with Alex's family. If this dynamic persists after several expressions of this need (and possibly agreements to meet this need in the future), continuing this relationship may be a sign of codependence.

There are several options for addressing this. Here are four the come to mind:

1) Do nothing and stay unhappy. This isn't fun for anyone.

2) Leave the relationship now. This may provide immediate relief, but may also involve big and uncomfortable feelings, including guilt or doubt about whether leaving was the right thing to do.

3) Make an ultimatum and follow through. Some view ultimatums as manipulative. In my view, an ultimatum is only manipulative when there is no intention to follow through with ending the relationship. In this case, it involves expressing needs that must be met in order to continue the relationship. It can be helpful to collaboratively set a timeline for change to occur, along with very specific criteria for determining whether the needs have been met (Google SMART goals). If your partner doesn't agree to make changes, the relationship can end now.

4) Reexamine the needs and values that determine whether you are content in a relationship. Sometimes, the needs we have in relationships are based on past traumas or old values or beliefs that are no longer applicable to our lives today.

Upon further examination, we may find that we don't actually need the things we thought we did, or that it's okay to meet these needs through other relationships, like with friends or family.
We might also meet these needs through activities, like developing a skill, starting a new hobby, focusing on professional goals, or other confidence-building endeavors.

Either way, this involves self-work, which might look like deep reflection and self-examination, reading books about the influence of past experiences on present day relationships (e.g., books about attachment theory), or discussing these issues in individual or group psychotherapy.
If we develop significant insight about our needs in relationships, and the relationship remains unsatisfying, the option to end the relationship remains. This self-work will contribute to the success of future relationships.

Codependence is a challenging problem, but it isn't insurmountable. A relationship can start as codependent and end up in a better place, as long as both partners are willing to examine their  own behavior and make efforts to change. Sometimes those efforts don't result in enough change to save a relationship. That's okay.

The end of a relationship is not a personal failure. Identifying a mismatch in needs or values, addressing this mismatch, and ending a relationship if nothing changes is a sign of strength. Furthermore, collaborative exploration of these differences is a prerequisite for turning a codependent relationship into a fulfilling relationship for both partners.