Christa,
I am so sorry you are going through everything you are.. But to get to your question, the "confession" alone shows that he is sorry and regrets his actions. BUT! All that matters, is how YOU feel!
If you choose to stay and try to work things out, for the years you have spent together/the children you have, etc... For your own sake, I would suggest either hiring a P.I., or keep a close track of credit card/bank statements and especially phone bills... Any unknown numbers that come up, ask him casually "Hey Babe, Do you know who's number is (555...whatever....)?" After 24 years of marriage, you should be able to read his reaction..
AND if you are leaning towards divorce, there is nothing wrong with that. He hurt and betrayed you. But the main thing to remember is that men are just horny. Their purpose in life is to procreate, it's their biological need to "spread their seed", but it doesn't mean he ever loved her. With all of today's birth control technology you would think that they would calm the hell down! But, us women always have the deeper question "Does he Love HER!?"
No sweetie, he just had to show his ugly dominant male face! Men always listen to their head and not their hearts...
So it's your choice. Spend a few days away from home doing something you love, and really think about whether you're willing to stay... Is he really worth all the questioning you're going to go through, and the seducing you're going to do to win his place at home?
You decide, and whatever decision you make, will be the right one! Good luck girl, and we are all behind you!