My personal opinion is that 50/50 custody is NOT the best thing for any child. Even in the best of circumstances (both parents are reasonable and truly parent the child), the child has two homes, two rooms, two sets of rules, two dynamics and quite possibly not much consistency...how is that good? And when they become teens and the parents live in different towns, socializing with friends and having a job become BIG issues with scheduling, transportation, etc.
And in the worst of circumstances, the child may be neglected, or worse, all in the name of "being fair" to both parents. That is what happened to my son.
Children can have relationships with both parents, even if one has primary custody. Even when couples stay married, are they both at home with the kids for equal amounts of time? Rarely. One parent is usually (and I admit there are exceptions, but they are exceptions) the primary caregiver...it's just what happens.
Always, always, advocate for the best interest of your child and never give in just to be fair to the other parent. Always encourage your child to have a relationship with the other parent, whatever that relationship may be, but you don't have to give up custody to do that.
Unfortunately, most states now advocate 50/50 custody (that's what happened to us), so if you end up in court, that's what you will likely get. If at all possible, work things out without more court and within your custody agreement. Dad wants to be more involved? You both attend sports, music, school events, etc. She has an activity every Tuesday night? Maybe dad can pick her up and take her to it. There's no better place to talk with a teen than in the car...you have their attention! Be creative an encouraging...so long as it does not harm your child...but I would never advise 50/50 custody. Ever.
And by the way...my daughter, who was 14 when we divorced, did not have a relationship with him after he left because he rather dropped out of our lives for almost three years. She made it through high school in honors classes, played sports, became a life guard, went to college (her dad didn't even go to her graduation!), met a great guy, got married and is now expecting their first baby. She has a limited relationship with her dad to this day, but she made it through her teen years just fine.