Advice?

My ex gets our son for about 5-6 hours every Sunday WITH his parents present. (He has a short temper and before i left him would yell at my son and even push him out of his way if he was moving too slow, etc... my son was only 1)

After today when I went to pick him up he said he wants to start having our son spend the night because he’s his son too. (I’m 100% sure he’s just trying to make me think staying away from him isn’t worth it) I told him no, though I will admit he’s been doing a little better with him.

When I got my son home he had a wet diaper (just pee) and he had poop around his crack and in his folds. I could see poop before I even started wiping him. Like his dad barely wiped him after a poopy diaper. I had been considering giving him more time but now I feel even more strongly that he should not be alone with my son.

Am I over reacting?