It depends on the situation and your feelings towards her and her actions.
First and foremost we pray that God forgives our sins, and strengthen us to the degree that we are able to forgive.
It is an unbearable situation, and I can only imagine the pain you are going through. You should give yourself credit for reaching out and seeking help rather than acting in a moment of anger, like the Prophet (S) said, ‘Anger is a smouldering ember [kindled by] Satan.’ [Bihar al-Anwar, v. 73, p. 265, no. 15]. All of our actions and words have consequences, and it is an admirable trait that you are seeking counsel before reacting to the news of your wife’s adultery.
Whether you should forgive her or let go is entirely up to you. I would try to understand the reasons behind her actions as they may be a result of her being unhappy or struggling with something. In longterm relationships we might overlook the signs that the other person is unhappy, and we might get used to the person being there, resulting in us not paying the same attention as we did in the beginning of the relationship. Relationships demand a lot of work, especially communication exercises, compassion, respect and patience.
If you decide it is worth fighting for, you must be sure that she is determined to work on the relationship as much as you are. This, of course, includes not cheating again, but also acknowledging the mistakes one made. You have to find the reasons behind your current situation, where did it go wrong? It might not be a specific situation or time, but minor incidences adding up to this. Therapy is a good way to deal with past trauma and you might even find communication courses beneficial. You must be able to forgive her, let go and work on the mistrust. If you can’t, it will continue to create unbalance in the relationsship. We must be able to forgive in order for the other part to move on, and leave behind their misdeeds. If we can’t forgive, it is better to take some time apart, dealing with one’s emotions.
When we are trying to change, to improve ourselves and rise from the darkness of our misdeeds, it is unhealthy for our growing process that we are reminded of the actions we are trying to distance ourselves from. She will not be able to move past that sin if you are reminding her, which is a natural result of being hurt. If you want to work on it, you both have to possess a sincere interest of understanding each other. If one is going into a dialogue with pain, mistrust and accusations, one will not succeed. One must go into a dialogue with a sincere desire of understanding the other part, and respecting their version of the truth, even though it might be different from one’s own version.
If you on the other hand decide it is not worth fighting for you might find it beneficial to have a period of seperation before divorcing her. The Prophet (S) said, ‘The Prophet (S) said, ‘Shall I tell you who is the toughest and strongest from among you? The one who controls himself when he is angry.’[Nathr al-Durar, v. 1, p. 183]