My partner is still angry. Shouldn’t they be over it by now?
Anger needs to come out following an affair. The feelings of hurt and betrayal are usually so deep that it would be unnatural and unhealthy for no anger to be expressed. You should be prepared for outbursts of anger to continue for a while... probably for months. I know many couples who have come to very satisfying conclusions in their affair recovery who would tell you they experienced some outbursts of anger a couple of years after the affair. Be prepared for that.
Repairing your relationship will require some sacrifice from you. It is the cost required for rebuilding trust. You cannot expect your spouse to get over this quickly, so you will have to be willing to deal with their pain and disconnection (often expressed in sadness and anger) while they heal. This will be uncomfortable for you, but it's part of the process.
If your marriage is going to recover, there should, eventually, be a diminishing of anger. After the first month or so of initial expressions of grief and outrage, anger tends to decrease in intensity and frequency. If, after that time, there still seems to be no diminishing of anger, then something is getting in the way. In those cases, these are the things I begin to investigate:
Is there more to the affair story that is still being hidden? It is incredible how many times unconfessed secrets continue to sabotage the recovery effort. This is one reason why getting the whole truth out at the start of recovery is very important If something is still hidden, you need to consider coming completely clean.
Has the affair partner expressed genuine sorrow and grief for what they did? Are they willing to offer ongoing empathetic responses to the wounded spouse rather than insisting they "get over it and move on"?
Has the affair tapped into hurt or trauma from the injured partner's past? If so, their emotional response is amplified, and they will likely need help working through past and present issues.
Are both partners honestly committed to the process of marriage recovery? Suppose either one is just "playing the game" of recovery while having no honest intent to make the marriage work. In that case, anger is simply an ongoing expression of something that will never be resolved while playing this game.
Is the betrayed partner unwilling to acknowledge his/her part in marriage problems? It's easy to focus on the failures of the affair spouse, but at some point, the betrayed spouse must be willing to take an honest look at how they contributed to the condition of the marriage. This, by the way, is in no way accepting responsibility for the affair. But if, after the initial normal anger reactions, the betrayed spouse stays angry (continues to accuse, continues to obsess over the same affair issues) and remains in this pattern for months and years, it is usually an indication of an unwillingness to assume any responsibility for the state of the marriage.
Both partners must be willing to look beneath their anger to see the deeper emotions at play. Anger is an easy emotion to access, but it usually indicates something more significant: fear, hurt, shame, or feeling powerless/inhibited.