On relationships

I have had 4 hours sleep, thinking about whether to write this piece. My father would disagree with me about writing it, but I feel that a problem shared is a problem halved, so sorry Dad, but this has to be done.
John's Mum and I first got together some 15 and a half years ago. I haven't blogged about her much before, purely because that's one part of my life my readers don't really need to know about. There have been times where she's got a mention, but this is because she's helped or abetted where the story is to be written. We both have a lot in common, and this is something that is vital for a relationship to last this long (are you taking notes Dad?). We both enjoy similar music, we both enjoy the same types of films. We both have a passion for cooking (she's a qualified chef) and so when it comes to evenings together we often find plenty of things to do. She's also the Ying to my Yang, whereupon she deals with the household finances, whilst I'd quite merrily blow the week's money on some reduced helicopter in Maplins. I deal with all the bills, whilst she makes sure we have the money to pay for them.
We have our ups and downs. 11 years ago, she declared she no longer loved me. We worked at it, and were soon back to our old selves. I slumped into real depression about 5 years ago, when I felt that I was unloved. She'd say she loved me, but I felt that it just wasn't the case. Whilst in this darkened phase, I have to admit I nearly strayed. On more then one opportunity I had the chance of extra marital affairs, but all the time the fact I was thinking with my balls and not with my brain made me back off. Perhaps it was a real 'dark cloak' of depression, but the fact was we came out of it ok.
4 weeks ago, Chris went home (Greenock, Scotland) to her mother's for a week. When she returned, she was genuinely pleased to be home and had genuinely missed me. We'd both missed her as well, and things settled down with renewed life. Whilst she was away, she'd told me she'd managed to get in touch with her ex-boyfriend, her first love, and the man who took her virginity. If I'm honest, I was very uneasy about this, but I told her that as long as they were just friends, I was cool. She told me it was ok, and I took her word for it.
The signs were not good. Her mobile was always bleeping, to let her know she'd got messages.
"Who's that from?" I'd ask, knowing full well it was Sam.
"BT," she'd say.
We'd had massive phone bills in the month she'd been back. £60 on the landline, £35 of which were phonecalls to Sam. £100 on her mobile (and that's what I know of) what with texts and calls made. She also started to use Messenger a lot. John and I made jokes about the fact that she'd come in from work, and would be straight on her PC, talking to Sam. In fact, this is where I probably made a mistake. I (understandably, I think) started to get suspicious. And so I set up a logging system, where the conversations were logged on my PC. It took a few days to get right, but I now could sit safe in the knowledge that anything that was said could be checked out. I started to filter through the logs yesterday, and was not happy with what I'd seen.
"Does he know about us?" asks one.
"Do you love me, because I love you" says another.
"I can't believe we're finally going to be together, after all these years." says a third.
I spoke to my father about it. He said 'hang in there' and so I thought it would all be ok. But yesterday, I decided to nip it in the bud. The hardest part was actually a lot easier then expected. Telling John his Mum might have to leave was heartbreaking for me, but he knew why. He knew about Sam, but only that Mum had been speaking to him a lot. I told him that if she did leave, she might take him with her, but he said he'd rather stay with me.
And so, she returned from work last night. I confronted her with the evidence, and all the time she denied it. She didn't get upset, just a lot more angry. I told her that if she wanted to be with Sam, then to leave, but don't go around behind our backs. She just got stroppy, and said she'd stop contacting him. She then said get rid of her PC, because she's not going to use it any more. Last night we slept apart, and I laid in bed, not knowing what to do.
Today I feel an emotional wreck. I feel like a complete and utter shit, but no matter how many times I tell myself I've not done anything wrong, nothing makes the sour taste go away.