For me it's been all about sticking to my boundaries and not holding back from leaving if it becomes necessary in order to keep those boundaries enforced.

Keep in mind that codependents are internalizers - it is not like a codependent to blame others or abuse them. However, it is like a counterdependent to do this, which is like the polar opposite of codependency in which the person externalizes their issues. When dealing with a counterdependent one has to be extremely firm as they will run over every boundary in your book and not think twice about it if you let them. While codependency is all about "you", counterdependency is all about "me".

Thanks mxkx, for opening my eyes to counter-dependency! I never knew it existed. I thought this person was codependent because his actions were motivated by shame and guilt. I found this blurb online about counter-dependency:

On the counter-dependant side the counter-dependent person cannot face their shame and will do anything that it takes to avoid facing it which may involve virtually any type of addiction the most common of the traditional addictions being alcoholism. Another form of addiction even more common is the addiction to adrenalin in the form of anger at people in general and at their partner in particular. A counter-dependent person is afraid of opening up to another person possibly because they have been rejected or betrayed earlier in life but primarily because if they open up to another person they are also opening up to themselves and facing what they have refused to face. They try to bind their partner to them by threatening their partner and belittling them so that there partner will feel helpless and dependent on the counter dependent, they will adopt control behaviors.

In reality most co-dependent relationships have elements of both co-dependent and counter-dependent behavior in both co-dependents where each switches from one role to the other resulting in the push/pull effect often seen in codependent relationships, however usually each person in the relationship will predominately assume either the co-dependent or the counter-dependent role.

As a rule co-dependent people will subconsciously seek out counter-dependent people and counter-dependent people will subconsciously seek co-dependent people. Sometimes you do find two counter-dependents in a relationship where they are always fighting or two co-dependents in a relationship where they both feel aimless.

As a result of people being brought up with a male stereotype of men being strong, decisive and dominant and a female stereotype of women being caring, nurturing and submissive, then men are more likely to fall into the counter-dependent role and women are more likely to fall into a co-dependent role, although it must be noted that this is not always the case and there will be some relationships with a counter-dependent woman and a codependent man (the stereotypical hen pecked husband).