My experience, for what it's worth, (probably nothing since no two situations are alike) ended up where I wanted under the circumstances, specifically because I chose not to fight (I think). My daughter was about the age of what your daughter looks to be when I separated (14 years ago now...) Started out OK as we had an informal agreement where we split 50/50 custody, but when we went to formalize things suddenly my wife decided that she needed full time custody with an every other weekend deal for me. I think that the reality of it sets in, and the societal pressure for women in that situation makes them feel like they "just should" have full custody. Sounds miserable, right? I could have chosen to fight (knowing that she'd take it to the mat if I did) but in my case at least, I knew that whatever our problems, she wasn't pure evil, and I'd get more flies with honey. So, I rolled over, told her that she could have whatever she wants, but that my desire, regardless of what is formally decided was to have my daughter as much as possible, and way more than just every other weekend....but that she got to choose. Within about 2 weeks, we were back to 50/50. In our case, there weren't any other dudes (or chicks) involved, which helps keep things from getting dirty I think. And, I made the comittment to myself that I'd always live within 5 miles of my ex-wife, so that I'd be around even for the nights that my daughter wasn't with me, to pick up or drop off at school, help with homework with, etc. After a very short period of time, my ex-wife really relied on my to take my daughter more and more (her career started to take off) and to help out with driving / sports / homework even on my off days.
Every situation is differnt, and this only works in the case that the ex is a decent person deep down (in spite of what may be spewing out of her at the moment...) Food for thought anyway. My daughter is 17 now, just left for college this fall, and both my ex-wife and I are stumbling around figuring out where the hell all the years went with a smile on our faces from all of the good memories. It can work out for all involved is what I'm saying I guess.
In any case, best of luck with it, and even if it does get ugly now, it'll get better....