I haven't been on MN or AIBU for ages so please bear with me.
DS1 is 6 and sleeps at his dad's house every other weekend overnight. We've had problems in the past re access (ex-p used to be a substance user and pretty abusive towards me so we had to go to a contact centre) but over past 3 years he and the situation has really settled down and it's been amicable. 2 week's ago DS1 came home and said there had been a visitor to his dad's house and the visitor had slept on the sofa. Immediately I felt a bit inside so I very casually asked who the visitor was. DS1 didn't know his name or anything about him, just that he was a man. I'm hyper sensitive about the people who come into contact with my dc's because I was abused as a child so I asked ex-p and he said that the visitor was his gf biological father. She had never met him (he left when her mum was pregnant), so after tracking him down on FB (a month ago) he came to stay with them.
I didn't say anything to exp as I didn't really know what to think at the time but after mulling it over I'm not really happy that DS slept in a house with a stranger who neither ex-p or his gf knows that well. I know it's their house and I can't dictate who they have to visit but my gut reaction is that this is wrong. My DP has said that if I don't feel comfortable I should say something because my priority is DS. AIBU to talk to ex-p? Just need some advice and to guage reactions before I take it up with him. Thanks.