Alimony-signed separation agreement

My husband and I separated almost a year ago and worked with a mediator and have a signed separation agreement on file.

At the time, because I gave up a career to raise our children, we agreed that alimony would be provided indefinitely. His earning potential is about 5x mine. There were multiple affairs on his part which he has admitted to.

Firstly can he throw out our original separation agreement? And, secondly, I know that long term alimony is rare so do I stand a chance if we fight this in court?

We have been married for 17 years and have two children.

He can’t have the agreement thrown out, so to speak. In order to have it voided by a judge, he would have to show that it was signed under duress, or he was incapacitated at the time or one of the other contract defenses. But if you signed this after mediation, I doubt there are any viable defenses that would result in him being able to have the agreement struck down.

If he has obligated himself to the lifetime alimony, it is expected that he will pay it. Should he fail to do so you will need to sue him for breach of contract. A judge could relieve him of the obligation but he would have to have strong evidence that he was unable to make the payments anymore.