If you believe he might not be the father, you must request that he and the child submit to DNA paternity testing in which they take a buccal swab from the inside of the cheek and test it against each other to determine whether he is the father or not. If he is found to be the father, which is the very first step, then he will be ordered to pay child support (which is mandatory under CO law) and will be given parenting time rights with the child. If there is a question about paternity, ask for the paternity test. You need to make sure for both the father and for the child. Child support is made retroactive to birth and he would be required to make a payment arrangement on the back support.
I agree with Mr. Lenoi and would add that if there is legal presumption of paternity, then the courts will give parenting time and order child support immediately and you have the burden of proving the presumed father is not, in fact, the father. Presumptions of paternity arise most commonly when the child was born during a marriage or when the presumptive father signed the birth certificate.
Additionally, a person who acts as a parent even if they are not the parent can gain rights under the psychological parent statute. In order to be a psychological parent, the individual must have acted as a parent for six months and it must not have been more than six months since they last acted in that role.
If either of these scenarios apply to your situation, you may need to address them.
If you believe he may not be the father you may request a paternity test be done to establish paternity. After paternity is established the courts will address parenting rights and child support.