Should I pick my man or my daughter?

OK so a little back story. I've been with my partner nearly 3 years. He and my daughter (14) do not get on at all. They're always arguing and fighting. I'm always in the middle! I'm so fed up. I told him tonight I will always choose my daughter over him, I gave birth to her.! He doesn't think I discipline her enough, she is a mouthy teen but I pick my battles, I won't argue over petty things with her and I do tell her when she's in the wrong. I also try and sit and talk with my partner to see what we can do to make it work but he always ends up just getting angry... I feel like I can't win. They're both my whole world but this is killing me. He's walked out 4 times and left because he can't deal with her attitude any more. He really is a great man, he works hard at home and at work to provide. My daughter does have an attitude but no where near to what he makes out. I will never pick a man over my kids, ever! What do I do? I'm so lost!