The adulterers website Ashley Madison is expecting a massive 500 percent spike in sign-ups from women on the day after Mother’s Day. According to its data, there was a 442 percent increase in sign-ups (compared to the daily norm) after last year’s holiday, following an upward trend since 2010.

So what drives a woman to commit adultery after spending time with her family on Mother’s Day? Ann, a 42-year-old finance worker from Bergen County, NJ, who asked The Post not to use her last name, tells Jane Ridley her cheating story.

Opening the Mother’s Day card last year from my husband, Derek*, my heart sank. We’d been married for more than 15 years, and I was the mom of his two young children — but he hadn’t even thought to buy me flowers, let alone jewelry.

The whole run-up to Mother’s Day had been depressing. It made me feel old, like I was losing my sexiness. My marriage was stuck in a rut.

We’d gotten hitched when I was in my mid-20s. Things were great at first, but they started to fall apart almost as soon as our kids arrived.

Derek is only 48, but he might as well be in his 70s — he’s always tired and unmotivated. We have sex about once a week, though it’s hardly passionate. I never orgasm and just go through the motions.

Even though it was a big deal for me to cheat on Derek, I didn’t feel guilty. I finally felt alive and sexy again. - Ann

So, the day after Mother’s Day, I set up a profile on the cheaters’ website Ashley Madison.

I’d had a bit to drink and was feeling flirtatious, so I wrote how I was a voluptuous brunette looking to have an affair. Within minutes, I had responses from several guys, including a man called Tom with three children. He was 42, worked in the medical field and his marriage was even more dysfunctional than mine. He wasn’t having sex with his wife at all.

I met him less than a week later for lunch, at a restaurant about 40 minutes away from each of our homes. We ended up having a lot of fun drinking wine and getting to know each other.

We first had sex three weeks later, at a Best Western off Route 80. It sounds seedy, but it wasn’t. The sex wasn’t the best thing since sliced bread, just very intimate and passionate. I still wasn’t able to orgasm — in fact, I never have. But it got better as time went on.

Even though it was a big deal for me to cheat on Derek, I didn’t feel guilty. I finally felt alive and sexy again. I didn’t tell a soul — not even my best friends. It felt good having this big secret all to myself.

After that, Tom and I met for sex about once a month for six months, but then he started to flake out on me, canceling our meetings and making excuses. By then, I’d fallen in love with him. I never told him, because I knew deep down that he wanted to keep things casual and not leave his wife and family. To be honest, neither did I. Eventually, we stopped seeing each other.

After that, I met and slept with two other men through Ashley Madison, and I’m currently chatting online with a few guys. Derek and I still have sex about once a week, and I’m afraid to say the sex hasn’t improved. But now that I’ve had my affairs, it doesn’t bother me as much. If there is one thing I’ve learned from the experience, it’s that mothers need to pamper themselves and have fun elsewhere if they don’t feel appreciated at home.

* All the men’s names in the story have been changed.