If the parents were never married, but is no longer together, how does the father file for temporary custody? And after temporary custody, how will he go about filing for full custody? What is proof enough to a court that the mother is completely unfit to be the custodial parent?
First and foremost, you need to hire a well-seasoned family law attorney who is familiar with paternity, custody, support and the laws relating to unfit parents. As each state’s laws are a bit different, only a licensed attorney in the state where the child resides can answer these questions for you per your specific circumstances. However, there are some generalities that we can address.
As others have stated, if you are not the legal father then you need to be so. The first source I have posted is a link to an article explaining the various ways to go about establishing paternity. You should be aware that having established paternity does not necessarily give you custodial or visitation rights over the child. This is also explained in the article.
To answer your question in relation to the proof needed to prove the mother is unfit, you need to remember that most courts decide custody issues based on the ‘best interests of the child’ test. This test is made up different components which can differ from state to state. Components can include moral fitness of a parent and the respective environment offered by each parent.
Proof as to these components could include his testimony (and other first-hand witnesses) as to how much time each parent spends with the children and the activities each parent does with the children. If her activities outside the home are affecting the children, such as coming home intoxicated, this is also a factor.
Again, as these are state specific you will need a family law attorney to help you determine what constitutes as evidence for proving that the mother is unfit to have custody of the child.
You should begin keeping a journal documenting what she does that you deem to be proving unfit. It will help you remember details when you begin the legal process.
You might want to check out DadsDivorce.com, even if you were never married, as they have tons of articles in relation to this topic and other topics surrounding children and custody. You might also want to chat with the guys on the forum section about this to see what experiences they might have to share with you.