On being the bigger man

Or woman, or person....
A situation has come up, once again, and I find myself torn. Life has landed me in a rather sweet position where work is concerned. I have the ability to set my own hours and leave when I want to. Now some of that is based on how busy things are, and some of it is offset by the guilt I feel when it seems I am not putting in enough time, but on the whole, if I need to leave early I can. I try not to take advantage of it. The staff work harder and are calmer when I am there.
My ex has already asked me to leave early four times this year and we are only six weeks in. Now he wants to get out of being a parent again (and mind you he only parents for 15 hours or less a week as it is). It wouldn't be hard to suck it up and switch things around to accommodate him. But, do I really want to? Is his Valentine's celebration with his fiance a good enough reason to? What do I get out of this situation? You might think that he has offered to keep her on his day off, or that he plans to take her for a weekend, but you really don't know him well in that case. Sometimes I really wish I was the bitch that people (namely his fiance and her family) think I am. I have tried to treat this split with grace and dignity. I refrained from taking him to the cleaners. I have financially bailed him out on more than one occasion since the divorce. I try not to complain or rant about his poor parenting in front of Wyn. I'll admit that being free of the mood swings and daily temper tantrums is pretty good compensation but at some point I would like to not have to be the bigger person.