So, my DS goes to his dads house (where he lives with his mother and brother) every other weekend from Friday night to Sunday night. Occasionally it is from Saturday to Sunday if ex cannot get DS to his club on Saturday morning. Ex is barely present at drop off/pick up and has probably been there about 5 times in the past year, his mother does it all.
Last year ex and I agreed on the every other weekend, plus ex was allowed to see DS one night a week (not a sleepover as DS couldn't get to school the next day) and additional days here and there (school holidays, family events on that side etc). Ex also demanded every other Christmas and for DS to go over on ex's birthday but never mentioned seeing DS on his birthday 
So far ex has never asked for additional days, instead I've pointed out it is possible and he agreed to keep DS. Other times his mother has asked for an extra day during my weekend due to family events, again I've agreed.
Ex has never asked to see DS during the week.
Ex cancelled Christmas this year and said DS could just stay at home (I was thrilled, but ever the hullabaloo he caused earlier in the year about alternative Christmases I was a bit puzzled).
Ex is also very lax when it comes to arranging times for DS to get collected/dropped off for visits. More often than not it gets to the Thursday night and I have to text him to remind him his son is due to come over that weekend and could he please let me know if this is still the case.
We had a whole host of issues in the past (DS is only 6 and we split when DS was 7 months, he was NC until DS was about 3 but DS still saw his gran etc and then very sporadic contact until late 2015/this agreement).
Now it's the first weekend of 2017 and DS is due to go to his dads tomorrow. He was supposed to be with ex 23rd-25th but went on 26th to 29th instead (ex was working 28th and 29th so DS was with his gran). Then with me NYE weekend. Now he should be over there.
Would it be unreasonable of me to just not text him and arrange anymore? If he doesn't arrange by the Thursday night then just not have DS go over? I'm sick of planning for him and chasing him up: he's a 25 year old man! He can arrange to see his gf, days out with friends and holidays but cannot take a few minutes to check when his son is coming over and arrange something!