Before I start I just want to tell you I have never stopped DS from having contact with his dad, I have always organised it myself! His dad has even lied to not come before
The problem is his dad has always come to my house to see DS as he has been happy to do so.
We split when DS was about 3 months because I found out he had cheated on me when pregnant, he also didn't want DS to even be born and has admitted he has never made any attempt to even come live with us when we were together (better job, learn to drive as we can't survive without where we live)
He isn't a bad dad but he isn't a good one either. He sits watching tv with him and that's pretty much it 
We have both been very happy with the arrangement that he sees DS here and he has never said he wants it any other way.
He lives at home with his parents who are a 30 min drive away and his family have never travelled to see DS once in his life. After 5 months of not seeing DS they finally made the effort to come for the first time. Therefore I took DS to see them a while later and have seen they have done the spare room up for DS and their other grandson.
DS's dad said they are going to get a cot for him to sleep over and in terrified 
DS stops at my parents when I work and I feel comfortable with that. But the thought of DS stopping at his dads (his parents house) scares me to death.
His dad doesn't wake when DS cries and his mum has serious mental health issues.
They haven't yet asked for DS to stop there but I'm waiting for it now and it seriously scares me.
I don't know what to do 
I realise I can't stop it but I'm so upset about it. I'm not PFB about DS at all but there's just a bad feeling I get about him staying at their house
Has anyone got any advice to help me through this?