You live with someone long enough, in the eyes of the law you're common-law. So referring to the GF as the "wife" doesn't mean much.
JayDub, I don't know where you live so the legalities may vary a bit, but do this now:
1. Find a social worker you can trust. Explain the situation and ask what steps you need to take going forward to protect the relationship between yourself and this little girl.
2. Track everything (and I mean everything) from today forward. If you interact with your ex, write down what was said and the time the conversation started. Conversations with the mom. With your daughter. With the social worker I mentioned before. It is a huge pain in the ass, but eventually it becomes second nature and believe you me - it will save you
much grief and heartache in the long run.
3. If you can limit your conversation with your ex to e-mail, do it. If you can't, track the nature and time as stated in #2. Remember, you need to be able to track those interactions and email is forever (thx Google).
4. Hit up a lawyer. Most family lawyers will provide you with an initial 30 minute consultation for free, so take the information you've been tracking and hit as many as possible until you find somebody that you click with. The money won't necessarily be an issue if you can engage in
collaborative divorce
mediation. Even if you think you and the missus are going to get back together,
do not wait to get legal advice.
5. Under no circumstances engage in any heated conversation with your ex or her family. To the point of stoicism. If anybody is going to provide ammunition for court, let it be her. Plus if you do end up getting back together, it's a lot easier to swallow words better left unsaid. You don't have to eat shit, but it takes two to fight. Always look at the big picture and how your actions at that moment could affect that, take a deep breath or two and reel it in. You'll have other opportunities to vent your frustration.
Double down on your budget as best as you can. Internet sentiment is cheap, but rest assured that I feel for your situation. Good luck.