Ex really does think I'm daft. I'm sorry but I am never going to believe he wants whats best for DS because the bottom line is he only ever wants whats best for him. 
To cut a long story short he has just dropped DS off and asked if he can change his overnight from a saturday to a friday 'for DS's sake' as his big brother doesn't often go on a saturday anymore. Ex has a new girlfriend who's dcs go and see their dad on a weekend - shall we have a guess what night she is child free?? 
He is such a twerp.
DS has only ust gone back to sleeping there and ex really needs to build his relationship with DS from the ground up - he is very selfish, doesn't bother with him, play with him, etc. Last two visits he has made an effort with DS (just generally playing with him when he's there).
He has already cut his two overnights a week down to one. He messes about changing days round so he can go out and such like even though DS is autistic and hates change and likes to have a routine.
Urgh. I really want to get it off my chest to him but I know it's pointless.