Needing Help With Child Custody?

Here's the scoop, my ex boyfriend and I decided to end our relationship about a month ago, I moved 400miles away with our 1yr old daughter. We have no legalities when it comes to custody or child support or anything like that, he just comes to see her when he wants to. Well, today we talked and he found out that I'm dating someone casually, nothing serious. And since he's found this out he's really flipped out on me about it and has decided he's going to take our daughter from me because he doesn't agree with me dating other people already. Basically, what I'm wanting to know is, how do I keep that from happening? He's a great dad when he wants to be, dont get me wrong, I just want to make sure that he doesn't take her from me and I never see her again. Which is what he's threatening right now. Any advice would be great. Thanks!