A few days ago just before school I needed to do online homework so I asked my mum if I could go on her laptop as mine is broken she said OK and came and put the password in and then went back up to bed with my stepdad ( they're engaged and he's the dad of my 3 year old sister and pretty much my dad since I don't know mine and he's been there since I was 4 I'm now 13 ) while I was on her laptop I noticed a tab at the bottom saying ' reasons not to stop ' just out of curiously to see what she was on about. It was a word document with Facebook messages that had been copied on there. The first few seems quite recent and said things like that one was too easy and want to come out this evening and stuff like that then the next ones were big paragraphs obviously not recent so I read most of it and they seemed to be having an argument. There was nothing said on there about my step dad or anything like that they seems to be arguing about their own thing. They were saying stuff like 'I didn't intend for you to actually mean something to me' and some other stuff I can't be bothers to say. My mum goes to roller derby and he one of the coaches and the derby team go on tours a lot and they really went to Birmingham for a weekend and I found in one of the messages from him saying 'I only wanted YOU in Birmingham'
My step dad also works in Germany for 2weeks a month so I think it started to happen when he was away. She does also go out a lot sometimes all through the night and me and my sister sleep over my nans but she's always told us its derby.
I'm not really sure what to do. I could just butt out of it but its really bugging me and I know my step dads going to get hurt and I just think cheating is wrong. I've told my friends and I'm not that close to my mum I'm closer to my nan so I really don't think I could saying thing to her but I'm just so suspicious every time she goes out and its really bugging me.
Sorry that its so long and poorly written but Im just really in need of some advice :/ thanks for reading I would be so grateful if you could help.

Why in the world would you tell your friends about this, it's none of their business.
It's none of yours either. You had no business reading stuff from your mom's computer.
If you didn't have the guts to confront your mom, you surely had no business telling your friends.

I agree with, Homegirl on this one. Not only is it wrong to snoop, come across it by accident or not, it's extremely rude to tell your friends about it. At your age, those kids will go home and tell their parents, or their friends, and now they'll all think your mother is a cheat. When really, there's a possibility she might not even be.

Never assume, only count it as an option of many. Especially in situations as sensitive as this.