Psychology today, define anger as a negative feeling, ranging from mild irritation to intense fury and rage,  “Good therapy” defines resentment as as anger experienced as a result of unfair treatment, which is  a relatively common emotion.

Bearing those definitions in mind, it is suggesting that there is a slight difference between both behaviors’ but they easily can intertwined into each other simple because of how a partner maybe impacted by the emotions that they are experiencing due to an unfair treatment.

 Resentment can also be viewed as a type of unspoken anger that can be detrimental to your relationships, because when you are not aware of what your spouse is going through and they only respond with body language and emotions that In itself creates a challenge in your relationship.  

Another point on the difference is that:

Anger is more of a strong feeling of displeasure. While Resentment, on the other hand, is more of a feeling of bitterness experience.

Note carefully that Resentment is not the same  as anger outburst. Rather, it is more of an emotion that keeps the mind locked in on the things that a spouse may not comfortable with over a period of time.

Anger in not always in a negative light, sometimes It is the concept of individuals that anger should not be not be experience in a relationship. But anger can be used sometimes for standing up for truth and injustice within the relationship.

The danger is when anger is used as a weapon, intimidation, to hurt your partner, to control each other or when it is stored up from un-resolves issues.

Here is an extra tip: One of the ways that you can know when anger is unhealthy is to observe your emotions when you are upset about something. The thing is a spouse should not have feelings of regret with expressing him or herself even if it was said with a slight anger emotion. Bear in mind if this is the case, it should be done with respect.  Anger done with disrespect and in a disruptive way is unhealthy for your marriage.

It is typical that, If you feel resentment you may also feel anger.

Resentment Left unattended, usually gets worse which will creates barriers to intimacy on all levels.