Mine had his about 2 and half years ago, after we had been married 31 years.
What did he do?
After a few months of weird gaslighting behaviour and being nasty to me I woke up one morning to find a letter on the doormat announcing he had run off with a Romanian woman he had met on the internet and gone abroad with her. She was the same age as our son.
He came back but carried on his affair with her visiting her frequently, being nasty to me etc.
What did I do?
I cried a lot, I lost a lot of weight because I stopped eating properly, I reached rock bottom and thought I'd never climb up again.
Then I got some counselling, I talked to friends, I talked to people on here, I talked to the Samaritans and 3 months after he'd run off I sued him for divorce because I wanted to start shaping my future not having it shaped for me.
But he hung around, he was still in my life, he was still living in our house with me.
A year after he started his affair I went to America to live with friends for five months and that time away from him allowed me the time to decide what I wanted and to detach myself from him. I read books about infidelity, abusive men, abandoned wives, mid life crises etc (I found one called 'Abandoned Wives by Vicky something a good one - I'll find the proper title for you). By the time I got back home I had properly moved on - I know longer felt vulnerable and worthless and I was starting to enjoy my independence.
Does he regret it?
His girlfriend dumped him and is now married to some other middle aged man she found. Our children and their spouses don't want anything to do with him, he;s had some health issues and is feeling rather sorry for himself. So yes I think he regrets it - he hasn;t said so, but he has lost a family who loved him - he thought everyone would 'get over it' and forgive him.
Meanwhile the divorce has been finalised, and I am buying a little house of my own.
Only you can decide whether you want to try to save your relationship, personally for me once the trust had been broken there was no going back, I was distressed and sad but I knew for me it was over. he asked me if we could try again after he was dumped - I said no.
But whatever you do, give yourself time, don't let him crowd you or harrass you do it on your terms and take back some of the control don't be a passive responder to his behaviour decide what you want, and make your own way, get some space from him where you can really think about things.
Being alone seems daunting, especially when it is thrust upon you, but I can honestly say I've never felt more free or more content and I am so much stronger - I know what I can do and truly believe in myself
Good luck