Backstory: we have two kids, just into their double digits years, and my ex and I have a 50/50 custody schedule since the separation. 1 week with me, 1 with him.

His friends are partiers/drinkers. Always have been, but he didn't go out with them much when we were together because they lived out of town. 

Since our separation, his two closest friends have moved back to our town again. So my ex is back to partying and drinking with them again.

Today my ex asked that I have the kids this Friday because another friend is coming into town and the guys are all going out drinking. My response was that I'd like to keep our weekend's with the kids consistent. So, I didn't tell him no, but honestly I think he shouldn't ask me to have the kids so he can go out drinking with his buddies. It's his week with the kids, after all. Anyway, his response made it clear that he's mad that I didn't agree. 

So, am I the asshole here? 