DP and I have been together for 9 years, I had two children before I met him and we have one together. My oldest is very nearly 17, about to go into her second year of college. Years ago her and DP used to get on really well but once she became a teenager they have had some difficulty getting on. She doesn't always want to listen to him, this often follows with the "you're not my dad" line but he tends to treat her differently, for example he'll buy things for the other two and not for her and he's a lot stricter with her. These are things I've tried to address and sort out between the two of them. However yesterday, whilst I wasn't home they got into a huge argument, which ended with him sending DD to pack her bags, which is when I got home, asked what was going on and all DP said was "she needs to go", I told DD she didn't have to go anywhere but she said she was going to stay at her friend's house tonight anyway and left. According to DP the argument was over her telling him how to look after DD2, I don't have DD's side of the story yet. Arguments with them seem to blow out of proportion but it's never gone that far. He acts about the same age as her at times like this but also uses the authority he has over her and takes it too far. I think if he had it his way she would have been made to move out by now, it's ridiculous. DD hasn't yet returned but said she will later today, when DP has left for his night shift, I know she's okay though just angry with him.