Excerpts from another good article (from Psych Central):

"When it comes to codependency, denial has been called the hallmark of addiction. It’s true not only for drug (including alcohol) addicts, but also for their partners and family members. This axiom also applies to abuse and other types of addiction. We may use denial in varying degrees:

First degree: Denial that the problem, symptom, feeling or need exists.
Second degree: Minimization or rationalization.
Third degree: Admitting it, but denying the consequences.
Fourth degree: Unwilling to seek help for it.

Thus, denial doesn’t always mean we don’t see there’s a problem. We might rationalize, excuse, or minimize its significance or effect upon us...

Denial of needs is a major reason codependents remain unhappy in relationships.

Frequently, partners of addicts or abusers are on the “merry-go-round” of denial. The addicts and abusers can be loving and even responsible at times and promise to stop their drug use or abuse, but soon start breaking trust and promises again. Once again apologies and promises are made and believed because the partner loves them, may deny his or her own needs and worth, and is afraid to end the relationship.

You might be wondering how to tell if you’re in denial. There are actually signs.

Do you:

Think about how you wish things would be in your relationship?
Wonder, “If only, he (or she) would . . .?”
Doubt or dismiss your feelings?
Believe repeated broken assurances?
Conceal embarrassing aspects of your relationship?
Hope things will improve when something happens (e.g., a vacation, moving, or getting married)?
Make concessions and placate, hoping it will change someone else?
Feel resentful or used by your partner?
Spend years waiting for your relationship to improve or someone to change?
Walk on eggshells, worry about your partner’s whereabouts, or dread talking about problems?"

Article:
Are You in Denial?