Recourse?

Is there any recourse once a separation agreement is signed and you then discover that your spouse was having an affair prior to the signing?

Depends on the recourse you are seeking, and the contents of your separation agreement.

A separation agreement is a valid and binding document, the discovery of an affair will not vitiate the agreement.

Wow. I’m amazed that there is no litigation avenue for a separation agreement. Obviously, had I known of the affair prior to our separation, I would have never signed the agreement as-is. I guess it not only pays to be a cheat, but the law also protects you if you hide such information.

There are litigation avenues if the agreement was procured by fraud or duress, or in the event of a breach of contract, however those scenarios are not applicable in this case.

If the separation agreement lacked a waiver of marital torts, then a marital tort could possibly be pursued and/or used as leverage to push amendments to the separation agreement, correct?

I assume you are referring to third party actions, and yes they can be used as leverage.

Well that I was left for a month with all of our children, one being a 5 year old, while also trying to maintain a full-time job. I’d call that duress! I was told that the two children that she wanted would not go with her until I signed the agreement. She used the pretense that she had to be sure she had money before she would take them. I was repeatedly told to stop dragging my feet and sign the agreement. It only took a month! I wondered why she was pressing me to sign. Obviously, now I know.

Actually duress is a tougher standard, in that you must be under the threat of imminent physical harm at the time the document is signed. (literally a gun to your head). I am sorry to hear you were taken advantage of.