DSD(just turned 18) broke up with her boyfriend in February after he cheated multiple times and treated her like shit. They had some nasty confrontations, including him letting himself in to our house, while DH and I were at work, to corner her and argue with her and later that week he told her to "just fuck off and go and kill yourself" (knowing full well she has MH issues and suffers with anxiety and depression).
She seemed to be getting on ok without him, spending time with friends, although some were mutual and the EX would inevitably turn up, mouthing off and causing trouble. He would follow her around and even used the "find my friend" app on her phone to keep track of her and turn up where she was.... but she was taking it in her stride and her friends were incredibly supportive.
I thought all was well until I discovered that she had taken him back and was acting as if nothing had happened 
DH and I have told her that he is not allowed in the house (we had issues with them shagging in her room when we were all in the house!! And yes I know that's what teenagers do, but NOT when her 6 year old sister is in the room below). She may have forgiven him for what he's done/put her through, but DH and I cannot forget what he did, especially telling her to kill herself. I DO NOT want him anywhere near my family (DD6 does not need to be exposed to this type of behaviour).
Are we being unreasonable to say that he is not welcome in our home?
She still sees him, stays at his house, hangs out with friends at the park and so on.
Have we drawn too firm a line? Should we renege on our decision and allow him to come in (bear in mind they'll be holed up in her room, and have already proven they can't be trusted to keep their pants on)?
I don't know how to deal with this!
Fingers crossed she comes to her senses and dumps him soon!
If you made it this far, thanks for reading 
any advice is welcome