'I thought I was in a happy relationship. Then I found my boyfriend's secret Facebook.'

As told to Ann Degrey.

For a while, I thought I'd finally found a grown-up relationship. The kind where we both had full lives, busy schedules, and didn't need to be in each other's pockets to feel close. Tom* was very attractive, attentive, and a great dad to his kids. He was really good at making me feel like I was the most amazing woman he'd ever met.

He worked in finance, travelled a lot for his job, and had shared custody of his two daughters with his ex-wife. From the start, he was honest about still being in contact with her, but said it was purely about parenting. I thought it was really nice that they were still friends. I respected that.

The last thing I wanted was any drama or jealousy.

He told me the marriage had ended two years ago and there was no going back.

Watch: The number one cheating sign that everyone misses. Post continues below.

So, when he'd travel "interstate for work" every few weeks, I never questioned it. He always messaged, called when he could, sent the occasional photo from his hotel room or at a conference. I missed him when he was gone, but I trusted him.

Until one day, I got a message from someone I never expected: his sister, Jo.

She and I had become friendly, and I always got the sense she liked me, so when she reached out, I thought it was just to catch up. But her first message was: "Hey... I think you need to see something. And I'm sorry in advance."

I had no idea what she meant. But then she sent me a screenshot from his Facebook page.

Not the one I knew, the one we were friends on. This was a second account. A private one. Only for family, apparently.

She'd been hesitant to say anything for a while but finally decided she couldn't keep quiet anymore.

I couldn't believe what I was seeing. Jo sent screenshots of various photos of Tom, not just with his kids, but with his ex-wife. Holding hands. Cuddling on the couch. At the beach together. One photo showed them kissing while the kids played in the background. In the captions he wrote things like, "Family time," and "Back where we belong."

My blood went cold. These photos were all recent. The dates lined up exactly with the weekends he claimed to be out of town for work. He hadn't been travelling. He'd been playing happy families with his ex. Right under my nose. I was mortified. I called him immediately. He didn't answer. Then he texted: "In a meeting, can I call you later?"

I replied: "Don't bother. I've seen the photos."

He called within seconds. He tried to spin it, of course. He said he and his ex had been "trying to rebuild the family dynamic for the kids." That it was "confusing," even for him. That he never meant to hurt me. He said they weren't officially back together, they were just "reconnecting" in a more realistic way, for the sake of the kids.

I asked him why he had to lie and why he didn't just end things with me if he wanted to give his marriage another try.

He said he didn't want to lose me. That he wasn't sure if things would work out with her, and I was his "safe space."

So I was clearly just some kind of emotional support blanket he could wrap himself in while testing the waters with his ex.

I blocked his number that night. I couldn't sleep. I just kept replaying every time he'd kissed me goodbye before a 'flight', every text he sent saying he missed me, every lie dressed up as honesty. It made me feel sick. Humiliated. Heartbroken.

And worst of all, I felt super stupid.

How had I not seen it? How did I fall for someone who was living a double life and didn't even blink while doing it?

What hurts the most is that I really loved him and I saw a future. I understood that he had kids and baggage, and I was willing to work around that. I thought we were building something real. Instead, I realised he was just using me.

I haven't spoken to him since.

His sister Jo checked in a couple of times to see how I was doing. I thanked her for telling me, even though it shattered me. At least now I know the truth.

It's taken time, but I've started to feel like myself again. I'm more cautious now. Less quick to believe someone's version of events. I'm very proud of myself for walking away. And I've learnt that if something doesn't feel right, it probably isn't. He wanted to have it both ways.

And for a while, he did.

But the truth always finds a way out.

And when it did, so did I.

The author of this article is known to Mamamia but has chosen to remain anonymous for privacy reasons.

Feature Image: Getty.