All my spidey senses were telling me that DP was cheating but he denied and denied and I was young and naive. One day we were doing some supermarket shopping and a girl I vaguely recognised walked up to us and they way they exchanged 'hellos' was like a fireworks display going off inside me - I just knew it was her. I asked who she was (mate's sister), and how long he'd known her (years) and asked how come I'd never heard of her as we'd been together about four years at this point, but he dismissed her as a nobody. In the end, with no evidence and wanting to believe him, I ignored my gut and let him talk me into a holiday we couldn't really afford on a Greek Island.
Arrive on Greek Island and from the first night, he kept disappearing to 'call his mum' and then 'check on his brother' etc etc. It was before mobile phones so he was going to a payphone just outside the hotel with a pre-paid card. On about the fourth night, he bought us both a drink then 'nipped off to call his sister as she wasn't feeling well according to his mum' and left me sat at the bar like an idiot for ninety minutes.
I went to look for him in the room, by the pool, outside the hotel and the phone box - nothing. I was so fucked off I decided to go for a walk and as I turned a corner, he was sat on a bar stool, holding hands and drinking a cocktail with supermarket girl. He tried the 'Oh my god, look who I bumped into!' for about thirty seconds, but even he knew it was ridiculous. They had basically arranged that she would fly out and stay in a smaller hotel in the same resort but with her mate, as they couldn't bare to be apart for even a week.
I was going to fly straight home but was so humiliated that I told him to move in to her hotel, and I spent the last three days crying and walking/swimming, so that by the time I flew home, I had done most of my snotty nosed howling.
Looking back, I wonder why on earth he didn't just finish with me and get together with her properly? We weren't married, no kids, it would have been easy....