Worried about step son

My step son is 7. My husband has had custody since he was 2. Recently his mom get every other weekends. I honestly can't stand my husband's baby mama. She doesn't even spend time with him on her weekends. She throws him to her boyfriend and his 2 grown ass sons who still stay at home(they're in their 30's) and leaves. She said it doesn't matter who she leaves him with on her time. Now he's always been a shy kid. But he's being more quiet than usual. He always gets super sad when it's time to go to his mom's house. He is having accidents while sleeping which annoyed my husband. My husband thinks he's just being lazy so he put him back in diapers to sleep in at night. Every time we ask how things are at moms he says nothing. I went in his room to tell him it's time for a bath and when I went to touch him he put himself in a ball until he realized it was me. He was a shy kid. Now he barely speaks at all and acts scared of everything.