I'll try to include as much info so as not to drip feed, so this may be a bit long.
I've been split from ex for about 2 year and for the first year he was massively unreliable when it came to having DS.
Since last December though things have improved quite a bit and we arranged that he'd have DS every other weekend, Sat morn to Sun evening, he then works Saturday of the weekends in between.
Things have improved but that's not to say things run smoothly; every 2-3 months he has 'car problems' so can't get to mine and when I suggest meeting halfway as I don't drive (so us both getting respective trains to meet in the big city) he says it's too much faffing, even though he must manage it to get to work when his car has issues 
Also DS had chickenpox in July so I asked ex if he could help by taking a day or two off as I couldn't afford an entire week off work. He got the Monday and Tuesday as annual leave so had DS, then the following weekend was his normal days with DS, but he didn't turn up and claimed to have forgotten all about it as he's had DS earlier in week.
Ex then didn't end up seeing DS until his next scheduled weekend a fortnight later, which was the first weekend in August.
He then had more car problems that resulted in him not being able to have DS for the rest of the month and saw him next on the weekend just gone (2nd/3rd Sept). So as you can see, still not most reliable.
Now he has just rang me to tell me that he'll be having DS every weekend as he wants to see more of him than he currently does, I told him that's unfair as I work Monday-Friday so all DS will see of me is the boring mundane bits of getting up early for nursery and then no sooner are we home and he's had tea and a bath it's time for bed.
Ex then started going on about how much CMS says he should pay as it's recently gone up due to his high commission earnings being a monthly regular, so I asked him if that had anything to do with wanting DS more often (more overnight stays = less maintenance for him to pay), he argued that it wasn't, it's just 'an extra bonus' for him (his words) so I suggested he stick to the EOWeekend arrangement but also has DS overnight through the week also, this way he sees him more and he can take part in the standard mundane parts of day to day life and parenting instead of taking all weekends from me.
So AIBU to refuse every weekend and say that EOW and one night during the week is all I'm willing to give?
Also, thanks for sticking with me if you read through all of that 