That's an awful turn of events for you Fth180519. It mus be a roller coaster of emotions, from getting married, to the early demise of that, his departure, the impact on your son and how things were going well when he returned.
It is brilliant that you have bounced back from your lowest moment.
It must be confusing and emotional to learn of this affair, as he is not who you thought him to be and what happened in your marriage is not what you thought.
I think you should take some time to take this news in and start the healing process. This man remains your son's father and whether on a false premise or not, you have given your son a great gift by getting along with his father.
What you descibe in causing pain to your husband, clearly is rvenge. Revenge means that you will have to focus on negativity and this is usually all consuming. By trying to cause hurt to him and the other woman, I do not think it will cause you to be happier. It is likely to impact your relationship with others, which will be a disadvantage for your son. Your son is only 3 and this woman could end up being his step mother. Acrimonity between them and you in the long run will impact you and your son, as I do not think you can stop them being in his life.
Ultimately, I think the people in your husband's and the other woman's lives will remain with them despite knowledge of the affair and will rationalise it. If they become estranged or hated, this will not help you anyway.
If they go to war with with ou, they may spin it so that you are portrayed as someone who led him to the affair.
Finally, I know this will be unpopular and hard to hear, but perhaps he is repeating what he saw in his family as I think physcologically there is a greater chance of history repaeting itself as we do what we see. I know there will be others whose parent/s cheated and they are very loyal.
For you, I think you should work on forgiveness. Take some time to feel a bit better and focus on what will make you and your son feel good. WHat will make you stronger in the long-term and happier. That is more edifing for the mond and soul. Plus you have done nothing wrong. Revenge leaves a nasty feeling as you have to get embroilled in scheming and cauing harm.
You're the innocent pary, remain so and be clean. I am sure your life will improve in you will feel much better in the future. At least you know what happened and are no longer being deceived.