My daighter and her half brother

i have a little girl who is 3 her father has a child around 7months old from another relationship he is no longer with the woman she has had him arrested numerous times over the past year saying he beat her and threatened her she is always in and out of his life with there child. a few months ago my lg told me ahe had met the bany and was around the lady  i asked him not to let her as they have a volatile relationship i also dont want lg to get a bond with the baby if there is no consistency and stability. she told me that she had been with them on saturday when she was at her dads but when inasked he lied and told me that it was a friend. I just want advice on what inshould do i have previously stopped him from taking her tonhis house and he will have contact here but everytine i start to trust him again he messes up he pits her around all his new girlfriends and when insay something he says im still in love woth him and jealous that is not true at all i am just looking out for my daughter her home life with me is very stable. I have tried to go to mediation but he wont have any of it i would never stop contact between them i just want him to respect how i feel on the situation and see its not about making him happy its about the best for our daughter. Sorry for long post