ExH and I have been separated for 8 years. In all that time, I have never said he can't see DD (now 16), even though he lets her down routinely - in fact I have often talked him into it, done more than my share of travel etc. I am a really firm believer in the importance of maintaining that daughter/father bond and have posted in that vein on here.
But on saturday I reached the end of my tether. After not seeing DD for 2 months (excuse after excuse - car trouble, xmas shopping etc etc) and not having her overnight for over 2 years, he suddenly decided he wanted her overnight on Sunday - the night before her first GCSE exam.
So I said no. He would never have got her to school on time and certainly wouldn't have encouraged her to revise (she should be out enjoying herself and getting pissed, according to him - higher education is a load of bollocks and you learn more from the 'university of life')He's been telling her for two months he can't pick her up due to an interrmittent and undiagnosable electrical fault with his car but now he can guarantee she will be there?
His wife has gone away for a week apparently and so suddenly he wants DD overnight - but Wednesday, Thursday, Friday or Saturday are no good. He has carpet fitters in. 
You should have heard how shocked he was when I said no. He then had a rant at DD and told her he wanted to strangle me, and that he wouldn't bother with her anymore as she clearly was going to turn out just like me and she should decide what was more important, exams or family. 