I'm a regular (ish!) but have namechanged as this doesn't make me look like a very nice person.
In my early 20s I had one of those love-of-your-life relationships. At first it was amazing, but after a couple of years, he (let's call him Bob) turned into a bit of a twat. He would invite me over to his house (him still living with parents, me with flatmates) then leave me downstairs/in bed and disappear off to play computer games, or - quite a few times - watch porn 
Of course this didn't go down well, but I was young and daft so put up with it. We moved in together, but a few months into the contract he walked out to go back to his parents as "mum does all the washing and cooking for me." Oh, and after an argument where I came home from a weekend away to find escort websites in the laptop history. (Claims it was his sleazy friends messing around )
Much more crap happened, eventually I broke it off and moved far faaaar away 
A year or so after we broke up, Bob got in touch to say he felt awful about the way he treated me, and could we still be friends. I was very unsure and kept him at arms length, but he was quite persistent and couldn't stop apologising for how he'd been, and he wished I'd forgive him and be with him again. I couldn't though, and was quite honest with him about that.
We stayed in touch, emails and occasional phone calls, lots of apologies from him, and telling me what a fantastic person I am (we also did have normal, friendly conversations, it wasn't like some kind of weird stalker..) When I got married to my DH, we still stayed in touch (with DH's knowledge) but we both kept things on a friendly basis. He'll still tell me I'm a brilliant person etc, but where it gets complicated is that I get the feeling that he thinks he's "above" me somehow, like he had the power in the relationship and he knew he could do anything, and I would just put up with it. Even now, I feel like he thinks I was a perfect, sweet stupid girlfriend, and he was a bit of a twat "lad".
What I've never told Bob, or anyone actually, is that in the last few months of seeing him I (stupidly, stupidly) had an emotional affair. No further than hand holding and the occasional hug. I knew full well that I was behaving like a shit, but I didn't care (which I know makes me sound like a complete cow - I should have just broken up with him.)
Can I tell him now please? As he's pissing me off. After spouting shite about how he'll always be there for me, he keeps ignoring me for months at a time. I really, really needed an ear, asked him for help and he didn't reply to me for 3 months. My fault for thinking he would be there, but still. No doubt he'll come back as usual in a few months all "I'm so sorry, you know I'm such a shit and you're so amazing, can we be friends forever??" Can I just say, no, no we can't. I wasn't a perfect amazing girlfriend, I was just as much of a twat as you, you just didn't know about it and I'm sick of hiding it. You didn't break my heart, I dumped you, so stop fucking apologising. I only stayed with you for so long because I was an idiot, and only found the courage to break up with you when you walked right past me as I was on a "date" with another man and you didn't even see me . I am a massive twat, I have conned you into being friends for years, and I don't like myself for it. Please stop being "nice" to me, and blaming yourself. Also, either be a friend properly, or fuck right off as I have no patience for your games any more.
God, I'm sorry for the length. Congratulations and 
if you made it this far 
But I think writing this down has saved me from phoning him and, well, leaving a shouty message on his answerphone as he wouldn't pick up for me would he 