I cried wolf a couple of times before it really ended too. Looking back, there was a manic period of about three months where I went from saying "that's it, it's over, I want you to go" to desperately trying to save it, sit down and talk about how we were going to work it out.
What pushed me in the end, was one evening when we'd talked (yet again) about honesty, trust, openness, etc. etc. and were just about to go to bed for a shag and then a niggling voice at the back of my mind reminded me that he hadn't shown me his bank statement to prove what he was saying was true. And I could no longer trust him to tell me the truth. I needed to see it to put my mind at rest. And he'd gone a thousand pounds overdrawn.
I just looked at it and laughed. And said "well I think this demonstrates that we don't have a partnership, do we?" I'd spent three months trying to come up with strategies to make our relationship work, mostly to do with honesty and open communication, and he'd spent 3 months going behind my back spending our money on who knows what and hiding it from me.
It was at that point that I faced the fact that he wasn't my partner, he was this very expensive stranger who happened to live in my house, shag me occasionally and do a bit of not very high-quality babysitting. At that point, I realised that an au-pair would be better value and less trouble.